U.S. patent application number 14/933441 was filed with the patent office on 2016-02-25 for memory system.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Kosuke HATSUDA, Hidenori MATSUZAKI, Junji YANO.
Application Number | 20160055080 14/933441 |
Document ID | / |
Family ID | 41055867 |
Filed Date | 2016-02-25 |
United States Patent
Application |
20160055080 |
Kind Code |
A1 |
YANO; Junji ; et
al. |
February 25, 2016 |
MEMORY SYSTEM
Abstract
A memory system according to an embodiment of the present
invention comprises: speed of processing for searching through
management tables is increased by providing a forward lookup table
for searching for, respectively in track and cluster units, from a
logical address, a storage device position where data corresponding
to the logical address and a reverse lookup table for searching
for, from a position of the storage device, a logical address
stored in the position and linking these tables.
Inventors: |
YANO; Junji; (Kanagawa,
JP) ; HATSUDA; Kosuke; (Tokyo, JP) ;
MATSUZAKI; Hidenori; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Minato-ku |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Minato-ku
JP
|
Family ID: |
41055867 |
Appl. No.: |
14/933441 |
Filed: |
November 5, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14275158 |
May 12, 2014 |
9213635 |
|
|
14933441 |
|
|
|
|
14021738 |
Sep 9, 2013 |
8762631 |
|
|
14275158 |
|
|
|
|
12529127 |
Oct 5, 2009 |
8554984 |
|
|
PCT/JP2009/052603 |
Feb 10, 2009 |
|
|
|
14021738 |
|
|
|
|
Current U.S.
Class: |
711/103 |
Current CPC
Class: |
G06F 2212/1044 20130101;
G06F 2212/7201 20130101; G06F 12/0246 20130101; G06F 2212/1016
20130101; G06F 2212/1048 20130101; G06F 12/0804 20130101; G06F
2212/7209 20130101 |
International
Class: |
G06F 12/02 20060101
G06F012/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2008 |
JP |
2008-051479 |
Claims
1. (canceled)
2. A memory system comprising: a nonvolatile memory that includes a
first area and a second area, the first area and second area
including blocks; and a controller configured to: manage data
stored in the first area according to a first management unit;
manage data stored in the second area according to a second
management unit, a size of the second management unit being larger
than a size of the first management unit, the size of the second
management unit being less than or equal to a size of a block; and
before performing a first processing, perform a second processing,
the first processing including reading valid data of the first
management unit from a first block of the first area and writing
the read valid data of the first management unit into a second
block of the first area, the second processing including reading
valid data of the first management unit from the first area,
integrating the read valid data of the first management unit into
data of the second management unit and storing the integrated data
of the second management unit into the second area.
3. The memory system according to claim 2, wherein the controller
is configured to: retrieve information associated with a logical
addresses by searching an address translation table with a physical
address of the first area; and determine the first block by the
information associated with the logical address.
4. The memory system according to claim 2, wherein in a case that
the number of blocks belong to the first area exceeds a first
threshold, the controller performs the second processing after
performing the first processing.
5. The memory system according to claim 2, wherein in a case that a
total amount of the valid data of the first management unit in the
first area is larger than or equal to a second threshold after
performing the second processing, the controller performs the
second processing again.
6. The memory system according to claim 5, wherein in a case that
the total amount of the valid data of the first management unit in
the first area is less than the second threshold after performing
the second processing, the controller performs the first
processing.
7. The memory system according claim 2, wherein when performing the
second processing, the controller determines an address area of the
second management unit corresponding to a storage capacity of a
certain number of blocks, and reads the valid data of the first
management unit that is included in the determined address area of
the second management unit.
8. The memory system according claim 2, wherein when performing the
second processing, the controller determines the valid data of the
first management unit to be read from the first area based on the
number of valid data of the first management unit that is included
in an address area of the second management unit.
9. The memory system according claim 8, wherein the controller
determines the address of the second management unit in an order of
a greater number of the valid data of the first management unit
that is included in the address of the second management unit, and
reads the valid data of the first management unit included in the
determined address of the second management unit.
10. The memory system according claim 8, wherein when performing
the second processing, the controller determines the valid data of
the first management unit to be read from the first area based on
whether or not valid data of the second management unit
corresponding to the address area of the second management unit
including the valid data of the first management unit in the first
area is stored in a block including an invalid data of the second
management unit in the second area.
11. The memory system according claim 2, wherein when performing
the second processing, the controller integrates the valid data of
the first management unit read from the first area with valid data
read from the second area.
12. A method for controlling a nonvolatile semiconductor memory,
the nonvolatile semiconductor memory including a first area and a
second area, the first area and second area including blocks, the
method comprising: managing data stored in the first area according
to a first management unit; managing data stored in the second area
according to a second management unit, a size of the second
management unit being larger than a size of the first management
unit, the size of the second management unit being less than or
equal to a size of the block; and before performing a first
processing, performing a second processing, the first processing
including reading valid data of the first management unit from a
first block of the first area and writing the read valid data of
the first management unit into a second block of the first area,
the second processing including reading valid data of the first
management unit from the first area, integrating the read valid
data of the first management unit into data of the second
management unit and storing the integrated data of the second
management unit into the second area.
13. The method according to claim 12, further comprising:
retrieving information associated with a logical addresses by
searching an address translation table with a physical address of
the first area; and determining the first block by the information
associated with the logical address.
14. The method according to claim 12, further comprising: in a case
that the number of blocks belonging to the first area exceeds a
first threshold, performing the second processing after performing
the first processing.
15. The method according to claim 12, further comprising: in a case
that a total amount of the valid data of the first management unit
in the first area is larger than or equal to a second threshold
after performing the second processing, performing the second
processing again.
16. The method according to claim 15 further comprising: in a case
that the total amount of the valid data of the first management
unit in the first area is less than the second threshold after
performing the second processing, performing the first
processing.
17. The method according claim 12, further comprising: in the
second processing, determining an address area of the second
management unit corresponding to a storage capacity of a certain
number of blocks, and reading the valid data of the first
management unit that is included in the determined address area of
the second management unit.
18. The method according claim 12, further comprising: in the
second processing, determining the valid data of the first
management unit to be read from the first area based on the number
of valid data of the first management unit that is included in an
address area of the second management unit.
19. The method according claim 18, further comprising: determining
the address of the second management unit in an order of a greater
number of the valid data of the first management unit that is
included in the address of the second management unit, and reading
the valid data of the first management unit included in the
determined address of the second management unit.
20. The method according claim 18, further comprising: in the
second processing, determining the valid data of the first
management unit to be read from the first area based on whether or
not valid data of the second management unit corresponding to the
address area of the second management unit including the valid data
of the first management unit in the first area is stored in a block
including an invalid data of the second management unit in the
second area.
21. The method according claim 12, further comprising: in the
second processing, integrating the valid data of the first
management unit read from the first area with valid data read from
the second area.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This present is a continuation application of and claims the
benefit of priority under 35 U.S.C. .sctn.120 from U.S. application
Ser. No. 14/275,158 filed May 12, 2014, which is a continuation
application of U.S. application Ser. No. 14/021,738, filed Sep. 9,
2013, which is a continuation application of U.S. application Ser.
No. 12/529,127, filed Oct. 5, 2009, now U.S. Pat. No. 8,554,984,
the entire contents of each of which is incorporated herein by
reference. U.S. application Ser. No. 12/529,127 is a national stage
application under 35 U.S.C. .sctn.371 of International Application
No. PCT/JP2009/052603, filed Feb. 10, 2009, which claims the
benefit of priority under 35 U.S.C. .sctn.119 from Japanese Patent
Application No. 2008-051479, filed Mar. 1, 2008.
TECHNICAL FIELD
[0002] The present invention relates to a memory system including a
nonvolatile semiconductor memory.
BACKGROUND ART
[0003] As an external storage device used in a computer system, an
SSD (Solid State Drive) mounted with a nonvolatile semiconductor
memory such as a NAND-type flash memory attracts attention. The
flash memory has advantages such as high speed and light weight
compared with a magnetic disk device.
[0004] The SSD includes a plurality of flash memory chips, a
controller that performs read/write control for the respective
flash memory chips in response to a request from a host apparatus,
a buffer memory for performing data transfer between the respective
flash memory chips and the host apparatus, a power supply circuit,
and a connection interface to the host apparatus (e.g., Patent
Document 1).
[0005] Examples of the nonvolatile semiconductor memory include
nonvolatile semiconductor memories in which a unit of erasing,
writing, and readout is fixed such as a nonvolatile semiconductor
memory that, in storing data, once erases the data in block units
and then performs writing and a nonvolatile semiconductor memory
that performs writing and readout in page units in the same manner
as the NAND-type flash memory.
[0006] On the other hand, a unit for a host apparatus such as a
personal computer to write data in and read out the data from a
secondary storage device such as a hard disk is called sector. The
sector is set independently from a unit of erasing, writing, and
readout of a semiconductor storage device.
[0007] For example, whereas a size of a block (a block size) of the
nonvolatile semiconductor memory is 512 kB and a size of a page (a
page size) thereof is 4 kB, a size of a sector (a sector size) of
the host apparatus is set to 512 B.
[0008] In this way, the unit of erasing, writing, and readout of
the nonvolatile semiconductor memory may be larger than the unit of
writing and readout of the host apparatus.
[0009] Therefore, when the secondary storage device of the personal
computer such as the hard disk is configured by using the
nonvolatile semiconductor memory, it is necessary to write data
with a small size from the personal computer as the host apparatus
by adapting the size to the block size and the page size of the
nonvolatile semiconductor memory.
[0010] The data recorded by the host apparatus such as the personal
computer has both temporal locality and spatial locality (see, for
example, Non-Patent Document 1). Therefore, when data is recorded,
if the data is directly recorded in an address designated from the
outside, rewriting, i.e., erasing processing temporally
concentrates in a specific area and a bias in the number of times
of erasing increases. Therefore, in the NAND-type flash memory,
processing called wear leveling for equally distributing data
update sections is performed.
[0011] In the wear leveling processing, for example, a logical
address designated by the host apparatus is translated into a
physical address of the nonvolatile semiconductor memory in which
the data update sections are equally distributed.
[0012] When a large-capacity secondary storage device is configured
by using such a NAND flash memory, in performing the address
translation, it is necessary to adapt small-sized data from the
personal computer as the host apparatus to the block size and the
page size of the nonvolatile semiconductor memory and write the
data. In such data management, if a unit of the data management is
a small size (e.g., the page size), the size of management tables
increases and does not fit in a main memory of a controller of the
secondary storage device. Address conversion cannot be performed at
high speed. In a search through the management tables, if search
processing takes long, an advantage of the flash memory that the
flash memory is fast compared with a magnetic disk device cannot be
effectively utilized. In this way, the size of the management
tables inevitably increases according to an increase in capacity of
the NAND flash memory as the secondary storage device. Therefore,
there is a demand for a method of reducing a capacity of the
management tables as much as possible and a method of increasing
speed of the search processing for the management tables. [0013]
[Patent Document 1] Japanese Patent No. 3688835 [0014] [Non-Patent
Document 1] David A. Patterson and John L. Hennessy, "Computer
Organization and Design: The Hardware/Software Interface", Morgan
Kaufmann Pub, 2004 Aug. 31
DISCLOSURE OF INVENTION
[0015] A memory system according to an embodiment of the present
invention comprises:
[0016] a first storing area as a cache memory included in a
volatile semiconductor memory;
[0017] second and third storing areas included in nonvolatile
semiconductor memories in which data reading and writing is
performed by a page unit and data erasing is performed by a
physical block unit twice or larger natural number times as large
as the page unit; and
[0018] a controller that allocates storage areas of the nonvolatile
semiconductor memories to the second and third storing areas in
logical block units associated with one or more of the physical
blocks, wherein
[0019] the controller executes: [0020] first processing for writing
a plurality of data in sector units flushed from the first storing
area to the second storing area as data in a first management unit;
[0021] second processing for writing a plurality of data in sector
units flushed from the first storing area to the third storing area
as data in a second management unit twice or a larger natural
number times as large as the first management unit; [0022] third
processing for flushing the data stored in the second storing area
to the third storing area as data in the second management unit;
[0023] fourth processing for selecting a plurality of valid data in
the first management unit stored in the second storing area and
rewriting the valid data in a new logical block; and [0024] fifth
processing for selecting a plurality of valid data in the second
management unit stored in the third storing area and rewriting the
valid data in a new logical block,
[0025] the controller includes: [0026] a forward-lookup first
management table for retrieving, from logical addresses in the
second management unit, first management information including
information including the logical block addresses indicating
storage positions in the second and third storing areas of the data
in the second management unit corresponding to the logical
addresses in the second management unit and storage positions of
the data in the second management unit in the logical blocks
designated by the logical block addresses and link information to
entries belonging to corresponding logical addresses in the second
management unit in a second management table; [0027] a
forward-lookup second management table that has an entry for each
of the logical addresses in the second management unit, the
forward-lookup second management table being a table for
retrieving, from logical addresses in the first management unit,
second management information including information including the
logical block addresses indicating storage positions in the second
storing area of the data in the first management unit corresponding
to the logical addresses in the first management unit and storage
positions of the data in the first management unit in the logical
blocks designated by the logical block addresses and link
information to logical block addresses registered in a fourth
management table; [0028] a reverse look-up third management table
in which, for each of the logical block addresses, third management
information including the link information to the logical addresses
in the second management unit registered in the first management
table is registered, the reverse look-up third management table
being a table for retrieving, from the logical block addresses,
addresses in the second management unit corresponding to data in
the second management unit included in the logical blocks
corresponding to the logical block addresses; [0029] a
reverse-lookup fourth management table in which, for each of the
logical block addresses, fourth management information including
the link information to the logical addresses in the first
management unit registered in the second management table is
registered, the reverse-lookup fourth management table being a
table for retrieving, from the logical block addresses, addresses
in the first management unit corresponding to data in the first
management unit included in the logical blocks corresponding to the
logical block addresses; and [0030] a fifth management table for
managing a correspondence relation between a plurality of physical
block addresses corresponding to a plurality of physical blocks and
logical block addresses corresponding to logical blocks associated
with the physical blocks, and
[0031] the controller executes the first processing to the fifth
processing based on the first to fifth management tables.
[0032] According to the memory system according to an embodiment of
the present invention, it is possible to provide a memory system
that can increase speed of the search processing for the management
tables and reduce a memory amount required for creation of the
management tables.
BRIEF DESCRIPTION OF DRAWINGS
[0033] FIG. 1 is a block diagram of a configuration example of an
SSD;
[0034] FIG. 2 is a diagram of a configuration example of one block
included in a NAND memory chip and a threshold distribution in a
quaternary data storage system;
[0035] FIG. 3 is a block diagram of a hardware internal
configuration example of a drive control circuit;
[0036] FIG. 4 is a block diagram of a functional configuration
example of a processor;
[0037] FIG. 5 is a block diagram of a functional configuration
formed in a NAND memory and a DRAM;
[0038] FIG. 6 is a detailed functional block diagram related to
write processing from a WC to the NAND memory;
[0039] FIG. 7 is a diagram of an LBA logical address;
[0040] FIG. 8 is a diagram of a configuration example of a
management table in a data managing unit;
[0041] FIG. 9 is a diagram of an example of an RC cluster
management table;
[0042] FIG. 10 is a diagram of an example of a WC cluster
management table;
[0043] FIG. 11 is a diagram of an example of a WC track management
table;
[0044] FIG. 12 is a diagram of an example of a track management
table;
[0045] FIG. 13 is a diagram of an example of an FS/IS management
table;
[0046] FIG. 14 is a diagram of an example of an MS logical block
management table;
[0047] FIG. 15 is a diagram of an example of an FS/IS logical block
management table;
[0048] FIG. 16 is a diagram of an example of an intra-FS/IS cluster
management table;
[0049] FIG. 17 is a diagram of an example of a logical-to-physical
translation table;
[0050] FIG. 18 is a flowchart of an operation example of read
processing;
[0051] FIG. 19 is a flowchart of an operation example of write
processing;
[0052] FIG. 20 is a diagram of combinations of inputs and outputs
in a flow of data among components and causes of the flow;
[0053] FIG. 21 is a more detailed functional block diagram related
to the write processing from the WC to the NAND memory;
[0054] FIG. 22 is a diagram of another configuration example of a
management table in a data managing unit;
[0055] FIG. 23 is a diagram of a diagram of a relation among
parallel operation elements, planes, and channels;
[0056] FIG. 24 is a diagram of another example of the
logical-to-physical translation table;
[0057] FIG. 25 is a diagram of an example of a BB management
table;
[0058] FIG. 26 is a diagram of an internal configuration example of
an FB management table;
[0059] FIG. 27 is a diagram of a correspondence relation between
logical blocks and physical blocks of the NAND memory;
[0060] FIG. 28 is a diagram of an example of an MS structure
management table;
[0061] FIG. 29 is a diagram of an example of an FS/IS structure
management table;
[0062] FIG. 30 is a detailed flowchart of an operation example of
write processing;
[0063] FIG. 31 is a flowchart of an example of an flush operation
of an IS;
[0064] FIG. 32 is a perspective view of an example of a personal
computer; and
[0065] FIG. 33 is a diagram of an example of system architecture in
a personal computer.
BEST MODE(S) FOR CARRYING OUT THE INVENTION
[0066] Exemplary embodiments of Memory System according to the
present invention will be explained below in detail with reference
to the accompanying drawings. The present invention is not limited
to the following embodiments.
EMBODIMENTS
[0067] Embodiments of the present invention are explained below
with reference to the drawings. In the following explanation,
components having the same functions and configurations are denoted
by the same reference numerals and signs. Redundant explanation of
the components is performed only when necessary.
[0068] First, terms used in this specification are defined.
[0069] Physical page: A unit that can be collectively written and
read out in a NAND memory chip. A physical page size is, for
example, 4 kB. However, a redundant bit such as an error correction
code added to main data (user data, etc.) in an SSD is not
included. Usually, 4 kB+redundant bit (e.g., several 10 B) is a
unit simultaneously written in a memory cell. However, for
convenience of explanation, the physical page is defined as
explained above.
[0070] Logical page: A writing and readout unit set in the SSD. The
logical page is associated with one or more physical pages. A
logical page size is, for example, 4 kB in an 8-bit normal mode and
is 32 kB in a 32-bit double speed mode. However, a redundant bit is
not included.
[0071] Physical block: A minimum unit that can be independently
erased in the NAND memory chip. The physical block includes a
plurality of physical pages. A physical block size is, for example,
512 kB. However, a redundant bit such as an error correction code
added to main data in the SSD is not included. Usually, 512
kB+redundant bit (e.g., several 10 kB) is a unit simultaneously
erased. However, for convenience of explanation, the physical block
is defined as explained above.
[0072] Logical block: An erasing unit set in the SSD. The logical
block is associated with one or more physical blocks. A logical
block size is, for example, 512 kB in an 8-bit normal mode and is 4
MB in a 32-bit double speed mode. However, a redundant bit is not
included.
[0073] Sector: A minimum access unit from a host. A sector size is,
for example, 512 B.
[0074] Cluster: A management unit for managing "small data (fine
grained data)" in the SSD. A cluster size is equal to or larger
than the sector size, and for example, is set such that a size
twice or larger natural number times as large as the cluster size
is the logical page size.
[0075] Track: A management unit for managing "large data (coarse
grained data)" in the SSD. A track size is set such that a size
twice or larger natural number times as large as the cluster size
is the track size, and for example, a size twice or larger natural
number times as large as the track size is the logical block
size.
[0076] Free block (FB): A logical block on a NAND-type flash memory
for which a use is not allocated. When a use is allocated to the
free block, the free block is used after being erased.
[0077] Bad block (BB): A physical block on the NAND-type flash
memory that cannot be used as a storage area because of a large
number of errors. For example, a physical block for which an
erasing operation is not normally finished is registered as the bad
block BB.
[0078] Writing efficiency: A statistical value of an erasing amount
of the logical block with respect to a data amount written from the
host in a predetermined period. As the writing efficiency is
smaller, a wear degree of the NAND-type flash memory is
smaller.
[0079] Valid cluster: A cluster that stores latest data
corresponding to a logical address.
[0080] Invalid cluster: A cluster that stores non-latest data not
to be referred as a result that a cluster having identical logical
address is written in other storage area.
[0081] Valid track: A track that stores latest data corresponding
to a logical address.
[0082] Invalid track: A track that stores non-latest data not to be
referred as a result that a cluster having identical logical
address is written in other storage area.
[0083] Compaction: Extracting only the valid cluster and the valid
track from a logical block in the management object and rewriting
the valid cluster and the valid track in a new logical block.
First Embodiment
[0084] FIG. 1 is a block diagram of a configuration example of an
SSD (Solid State Drive) 100. The SSD 100 is connected to a host
apparatus 1 such as a personal computer or a CPU core via a memory
connection interface such as an ATA interface (ATA I/F) 2 and
functions as an external storage of the host apparatus 1. The SSD
100 can transmit data to and receive data from an apparatus for
debugging and manufacture inspection 200 via a communication
interface 3 such as an RS232C interface (RS232C I/F). The SSD 100
includes a NAND-type flash memory (hereinafter abbreviated as NAND
memory) 10 as a nonvolatile semiconductor memory, a drive control
circuit 4 as a controller, a DRAM 20 as a volatile semiconductor
memory, a power supply circuit 5, an LED for state display 6, a
temperature sensor 7 that detects the temperature in a drive, and a
fuse 8.
[0085] The power supply circuit 5 generates a plurality of
different internal DC power supply voltages from external DC power
supplied from a power supply circuit on the host apparatus 1 side
and supplies these internal DC power supply voltages to respective
circuits in the SSD 100. The power supply circuit 5 detects a
rising edge of an external power supply, generates a power-on reset
signal, and supplies the power-on reset signal to the drive control
circuit 4. The fuse 8 is provided between the power supply circuit
on the host apparatus 1 side and the power supply circuit 5 in the
SSD 100. When an overcurrent is supplied from an external power
supply circuit, the fuse 8 is disconnected to prevent malfunction
of the internal circuits.
[0086] The NAND memory 10 has four parallel operation elements 10a
to 10d that perform four parallel operations. One parallel
operation element has two NAND memory packages. Each of the NAND
memory packages includes a plurality of stacked NAND memory chips
(e.g., 1 chip=2 GB). In the case of FIG. 1, each of the NAND memory
packages includes stacked four NAND memory chips. The NAND memory
10 has a capacity of 64 GB. When each of the NAND memory packages
includes stacked eight NAND memory chips, the NAND memory 10 has a
capacity of 128 GB.
[0087] The DRAM 20 functions as a cache for data transfer between
the host apparatus 1 and the NAND memory 10 and a memory for a work
area. An FeRAM (Ferroelectric Random Access Memory), PRAM
(Phase-change Random Access Memory), or MRAM (Magnetoresistive
Random Access Memory) can be used instead of the DRAM 20. The drive
control circuit 4 performs data transfer control between the host
apparatus 1 and the NAND memory 10 via the DRAM 20 and controls the
respective components in the SSD 100. The drive control circuit 4
supplies a signal for status display to the LED for state display
6. The drive control circuit 4 also has a function of receiving a
power-on reset signal from the power supply circuit 5 and supplying
a reset signal and a clock signal to respective units in the own
circuit and the SSD 100.
[0088] Each of the NAND memory chips is configured by arraying a
plurality of physical blocks as units of data erasing. FIG. 2(a) is
a circuit diagram of a configuration example of one physical block
included in the NAND memory chip. Each physical block includes
(p+1) NAND strings arrayed in order along an X direction (p is an
integer equal to or larger than 0). A drain of a selection
transistor ST1 included in each of the (p+1) NAND strings is
connected to bit lines BL0 to BLp and a gate thereof is connected
to a selection gate line SGD in common. A source of a selection
transistor ST2 is connected to a source line SL in common and a
gate thereof is connected to a selection gate line SGS in
common.
[0089] Each of memory cell transistors MT includes a MOSFET (Metal
Oxide Semiconductor Field Effect Transistor) including the stacked
gate structure formed on a semiconductor substrate. The stacked
gate structure includes a charge storage layer (a floating gate
electrode) formed on the semiconductor substrate via a gate
insulating film and a control gate electrode formed on the charge
storage layer via an inter-gate insulating film. Threshold voltage
changes according to the number of electrons accumulated in the
floating gate electrode. The memory cell transistor MT stores data
according to a difference in the threshold voltage. The memory cell
transistor MT can be configured to store one bit or can be
configured to store multiple values (data equal to or larger than
two bits).
[0090] The memory cell transistor MT is not limited to the
structure having the floating gate electrode and can be the
structure such as a MONOS (Metal-Oxide-Nitride-Oxide-Silicon) type
that can adjust a threshold by causing a nitride film interface as
a charge storage layer to trap electrons. Similarly, the memory
cell transistor MT of the MONOS structure can be configured to
store one bit or can be configured to store multiple values (data
equal to or larger than two bits).
[0091] In each of the NAND strings, (q+1) memory cell transistors
MT are arranged between the source of the selection transistor ST1
and the drain of the selection transistor ST2 such that current
paths thereof are connected in series. In other words, the memory
cell transistors MT are connected in series in a Y direction such
that adjacent ones of the memory cell transistors MT share a
diffusion region (a source region or a drain region).
[0092] Control gate electrodes of the memory cell transistors MT
are connected to word lines WL0 to WLq, respectively, in order from
the memory cell transistor MT located on the most drain side.
Therefore, a drain of the memory cell transistor MT connected to
the word line WL0 is connected to the source of the selection
transistor ST1. A source of the memory cell transistor MT connected
to the word line WLq is connected to the drain of the selection
transistor ST2.
[0093] The word lines WL0 to WLq connect the control gate
electrodes of the memory cell transistors MT in common among the
NAND strings in the physical block. In other words, the control
gates of the memory cell transistors MT present in an identical row
in the block are connected to an identical word line WL. (p+1)
memory cell transistors MT connected to the identical word line WL
is treated as one page (physical page). Data writing and data
readout are performed by each physical page.
[0094] The bit lines BL0 to BLp connect drains of selection
transistors ST1 in common among the blocks. In other words, the
NAND strings present in an identical column in a plurality of
blocks are connected to an identical bit line BL.
[0095] FIG. 2(b) is a schematic diagram of a threshold
distribution, for example, in a quaternary data storage mode for
storing two bits in one memory cell transistor MT. In the
quaternary data storage mode, any one of quaternary data "xy"
defined by upper page data "x" and lower page data "y" can be
stored in the memory cell transistor MT.
[0096] As the quaternary data "xy", for example, "11", "01", "00",
and "10" are allocated in order of threshold voltages of the memory
cell transistor MT. The data "11" is an erased state in which the
threshold voltage of the memory cell transistor MT is negative.
[0097] In a lower page writing operation, the data "10" is
selectively written in the memory cell transistor MT having the
data "11" (in the erased state) according to the writing of the
lower bit data "y". A threshold distribution of the data "10"
before upper page writing is located about in the middle of
threshold distributions of the data "01" and the data "00" after
the upper page writing and can be broader than a threshold
distribution after the upper page writing. In a upper page writing
operation, writing of upper bit data "x" is selectively applied to
a memory cell of the data "11" and a memory cell of the data "10".
The data "01" and the data "00" are written in the memory
cells.
[0098] FIG. 3 is a block diagram of a hardware internal
configuration example of the drive control circuit 4. The drive
control circuit 4 includes a data access bus 101, a first circuit
control bus 102, and a second circuit control bus 103. A processor
104 that controls the entire drive control circuit 4 is connected
to the first circuit control bus 102. A boot ROM 105, in which a
boot program for booting respective management programs (FW:
firmware) stored in the NAND memory 10 is stored, is connected to
the first circuit control bus 102 via a ROM controller 106. A clock
controller 107 that receives the power-on rest signal from the
power supply circuit 5 shown in FIG. 1 and supplies a reset signal
and a clock signal to the respective units is connected to the
first circuit control bus 102.
[0099] The second circuit control bus 103 is connected to the first
circuit control bus 102. An I.sup.2C circuit 108 for receiving data
from the temperature sensor 7 shown in FIG. 1, a parallel IO (PIO)
circuit 109 that supplies a signal for status display to the LED
for state display 6, and a serial IO (SIO) circuit 110 that
controls the RS232C I/F 3 are connected to the second circuit
control bus 103.
[0100] An ATA interface controller (ATA controller) 111, a first
ECC (Error Checking and Correction) circuit 112, a NAND controller
113, and a DRAM controller 114 are connected to both the data
access bus 101 and the first circuit control bus 102. The ATA
controller 111 transmits data to and receives data from the host
apparatus 1 via the ATA interface 2. An SRAM 115 used as a data
work area and a firm ware expansion area is connected to the data
access bus 101 via an SRAM controller 116. When the firmware stored
in the NAND memory 10 is started, the firmware is transferred to
the SRAM 115 by the boot program stored in the boot ROM 105.
[0101] The NAND controller 113 includes a NAND I/F 117 that
performs interface processing for interface with the NAND memory
10, a second ECC circuit 118, and a DMA controller for DMA transfer
control 119 that performs access control between the NAND memory 10
and the DRAM 20. The second ECC circuit 118 performs encode of a
second correction code and performs encode and decode of a first
error correction code. The first ECC circuit 112 performs decode of
a second error correction code. The first error correction code and
the second error correction code are, for example, a hamming code,
a BCH (Bose Chaudhuri Hocqenghem) code, an RS (Reed Solomon) code,
or an LDPC (Low Density Parity Check) code. Correction ability of
the second error correction code is higher than correction ability
of the first error correction code.
[0102] As shown in FIGS. 1 and 3, in the NAND memory 10, the four
parallel operation elements 10a to 10d are connected in parallel to
the NAND controller 112 in the drive control circuit 4 via four
eight-bit channels (4 ch). Three kinds of access modes explained
below are provided according to a combination of whether the four
parallel operation elements 10a to 10d are independently actuated
or actuated in parallel and whether a double speed mode (Multi Page
Program/Multi Page Read/Multi Block Erase) provided in the NAND
memory chip is used.
(1) 8-Bit Normal Mode
[0103] An 8-bit normal mode is a mode for actuating only one
channel and performing data transfer in 8-bit units. Writing and
readout are performed in the physical page size (4 kB). Erasing is
performed in the physical block size (512 kB). One logical block is
associated with one physical block and a logical block size is 512
kB.
(2) 32-Bit Normal Mode
[0104] A 32-bit normal mode is a mode for actuating four channels
in parallel and performing data transfer in 32-bit units. Writing
and readout are performed in the physical page size.times.4 (16
kB). Erasing is performed in the physical block size.times.4 (2
MB). One logical block is associated with four physical blocks and
a logical block size is 2 MB.
(3) 32-Bit Double Speed Mode
[0105] A 32-bit double speed mode is a mode for actuating four
channels in parallel and performing writing and readout using a
double speed mode of the NAND memory chip. Writing and readout are
performed in the physical page size.times.4.times.2 (32 kB).
Erasing is performed in the physical block size.times.4.times.2 (4
MB). One logical block is associated with eight physical blocks and
a logical block size is 4 MB.
[0106] In the 32-bit normal mode or the 32-bit double speed mode
for actuating four channels in parallel, four or eight physical
blocks operating in parallel are erasing units for the NAND memory
10 and four or eight physical pages operating in parallel are
writing units and readout units for the NAND memory 10. In
operations explained below, basically, the 32-bit double speed mode
is used. For example, it is assumed that one logical block=4
MB=2.sup.i tracks=2.sup.j pages=2.sup.k clusters=2.sup.l sectors
(i, j, k, and l are natural numbers and a relation of
i<j<k<l holds).
[0107] A logical block accessed in the 32-bit double speed mode is
accessed in 4 MB units. Eight (2.times.4 ch) physical blocks (one
physical block=512 kB) are associated with the logical block. When
the bad block BB managed in physical block units is detected, the
bad block BB is unusable. Therefore, in such a case, a combination
of the eight physical blocks associated with the logical block is
changed to not include the bad block BB.
[0108] FIG. 4 is a block diagram of a functional configuration
example of firmware realized by the processor 104. Functions of the
firmware realized by the processor 104 are roughly classified into
a data managing unit 120, an ATA-command processing unit 121, a
security managing unit 122, a boot loader 123, an initialization
managing unit 124, and a debug supporting unit 125.
[0109] The data managing unit 120 controls data transfer between
the NAND memory 10 and the DRAM 20 and various functions concerning
the NAND memory 10 via the NAND controller 112 and the first ECC
circuit 114. The ATA-command processing unit 121 performs data
transfer processing between the DRAM 20 and the host apparatus 1 in
cooperation with the data managing unit 120 via the ATA controller
110 and the DRAM controller 113. The security managing unit 122
manages various kinds of security information in cooperation with
the data managing unit 120 and the ATA-command processing unit
121.
[0110] The boot loader 123 loads, when a power supply is turned on,
the management programs (firmware) from the NAND memory 10 to the
SRAM 120. The initialization managing unit 124 performs
initialization of respective controllers and circuits in the drive
control circuit 4. The debug supporting unit 125 processes data for
debug supplied from the outside via the RS232C interface. The data
managing unit 120, the ATA-command processing unit 121, and the
security managing unit 122 are mainly functional units realized by
the processor 104 executing the management programs stored in the
SRAM 114.
[0111] In this embodiment, functions realized by the data managing
unit 120 are mainly explained. The data managing unit 120 performs,
for example, provision of functions that the ATA-command processing
unit 121 requests the NAND memory 10 and the DRAM 20 as storage
devices to provide (in response to various commands such as a Write
request, a Cache Flush request, and a Read request from the host
apparatus), management of a correspondence relation between a host
address region and the NAND memory 10 and protection of management
information, provision of fast and highly efficient data readout
and writing functions using the DRAM 20 and the NAND 10, ensuring
of reliability of the NAND memory 10.
[0112] FIG. 5 is a diagram of functional blocks formed in the NAND
memory 10 and the DRAM 20. A write cache (WC) 21 and a read cache
(RC) 22 configured on the DRAM 20 are interposed between the host 1
and the NAND memory 10. The WC 21 temporarily stores Write data
from the host apparatus 1. The RC 22 temporarily stores Read data
from the NAND memory 10. The WC 21 and the RC 22 may be configured
on different DRAM chips or other kind of memory chips described
above.
[0113] The logical blocks in the NAND memory 10 are allocated to
respective management areas of a pre-stage storage area (FS: Front
Storage) 12, an intermediate stage storage area (IS: Intermediate
Storage) 13, and a main storage area (MS: Main Storage) 11 by the
data managing unit 120 in order to reduce an amount of erasing for
the NAND memory 10 during writing. The FS 12 manages data from the
WC 21 in cluster units, i.e., "small units" and stores small data
(fine grained data) for a short period. The IS 13 manages data
overflowing from the FS 12 in cluster units, i.e., "small units"
and stores small data (fine grained data) for a long period. The MS
11 stores data from the WC 21, the FS 12, and the IS 13 in track
units, i.e., "large units" and stores large data (coarse grained
data) for a long period. For example, storage capacities are in a
relation of MS>IS and FS>WC.
[0114] When the small management unit is applied to all the storage
areas of the NAND memory 10, a size of a management table explained
later is enlarged and does not fit in the DRAM 20. Therefore, the
respective storages of the NAND memory 10 are configured to manage,
in small management units, only data just written recently and
small data with low efficiency of writing in the NAND memory 10.
The techniques using the "small units" together with the "large
units" in the SSD 100 are described in the International
Application No. PCT2008/JP/073950, the entire contents of which are
incorporated herein by reference.
[0115] FIG. 6 is a more detailed functional block diagram related
to write processing from the WC 21 to the NAND memory 10. An FS
input buffer (FSIB) 12a that buffers data from the WC 21 is
provided at a pre-stage of the FS 12. An MS input buffer (MSIB) 11a
that buffers data from the WC 21, the FS 12, or the IS 13 is
provided at a pre-stage of the MS 11. A track pre-stage storage
area (TFS) 11b is provided in the MS 11. The TFS 11b is a buffer
that has the FIFO (First in First out) structure interposed between
the MSIB 11a and the MS 11. Data recorded in the TFS 11b is data
with an update frequency higher than that of data recorded in the
MS 11. Any of the logical blocks in the NAND memory 10 is allocated
to the MS 11, the MSIB 11a, the TFS 11b, the FS 12, the FSIB 12a,
and the IS 13.
[0116] Specific functional configurations of the respective
components shown in FIGS. 5 and 6 are explained in detail. When the
host apparatus 1 performs Read or Write for the SSD 100, the host
apparatus 1 inputs LBA (Logical Block Addressing) as a logical
address via the ATA interface. As shown in FIG. 7, the LBA is a
logical address in which serial numbers from 0 are attached to
sectors (size: 512 B). In this embodiment, as management units for
the WC 21, the RC 22, the FS 12, the IS 13, and the MS 11, which
are the components shown in FIG. 5, a logical cluster address
formed of a bit string equal to or higher in order than a low-order
(l-k+1)th bit of the LBA and a logical track address formed of bit
strings equal to or higher in order than a low-order (l-i+1)th bit
of the LBA are defined. One cluster=2.sup.(l-k) sectors and one
track=2.sup.(k-i) clusters.
Read Cache (RC) 22
[0117] The RC 22 is explained. The RC 22 is an area for temporarily
storing, in response to a Read request from the ATA-command
processing unit 121, Read data from the NAND memory 10 (the FS 12,
the IS 13, and the MS 11). In this embodiment, the RC 22 is managed
in, for example, an m-line/n-way (m is a natural number equal to or
larger than 2.sup.(k-i) and n is a natural number equal to or
larger than 2) set associative system and can store data for one
cluster in one entry. A line is determined by LSB (k-i) bits of the
logical cluster address. The RC 22 can be managed in a
full-associative system or can be managed in a simple FIFO
system.
Write Cache (WC) 21
[0118] The WC 21 is explained. The WC 21 is an area for temporarily
storing, in response to a Write request from the ATA-command
processing unit 121, Write data from the host apparatus 1. The WC
21 is managed in the m-line/n-way (m is a natural number equal to
or larger than 2.sup.(k-i) and n is a natural number equal to or
larger than 2) set associative system and can store data for one
cluster in one entry. A line is determined by LSB (k-i) bits of the
logical cluster address. For example, a writable way is searched in
order from a way 1 to a way n. Tracks registered in the WC 21 are
managed in LRU (Least Recently Used) by the FIFO structure of a WC
track management table 24 explained later such that the order of
earliest update is known. The WC 21 can be managed by the
full-associative system. The WC 21 can be different from the RC 22
in the number of lines and the number of ways.
[0119] Data written according to the Write request is once stored
on the WC 21. A method of determining data to be flushed from the
WC 21 to the NAND 10 complies with rules explained below.
[0120] (i) When a writable way in a line determined by a tag is a
last (in this embodiment, nth) free way, i.e., when the last free
way is used, a track updated earliest based on an LRU among tracks
registered in the line is decided to be flushed.
[0121] (ii) When the number of different tracks registered in the
WC 21 exceeds a predetermined permissible number, tracks with the
numbers of clusters smaller than a predetermined number in a WC are
decided to be flushed in order of LRUs.
[0122] Tracks to be flushed are determined according to the
policies explained above. In flushing the tracks, all data included
in an identical track is flushed. When an amount of data to be
flushed exceeds, for example, 50% of a track size, the data is
flushed to the MS 11. When an amount of data to be flushed does not
exceed, for example, 50% of a track size, the data is flushed to
the FS 12.
[0123] When track flush is performed under the condition (i) and
the data is flushed to the MS 11, a track satisfying a condition
that an amount of data to be flushed exceeds 50% of a track size
among the tracks in the WC 21 is selected and added to flush
candidates according to the policy (i) until the number of tracks
to be flushed reaches 2.sup.i (when the number of tracks is equal
to or larger than 2.sup.i from the beginning, until the number of
tracks reaches 2.sup.i+1). In other words, when the number of
tracks to be flushed is smaller than 2.sup.i, tracks having valid
clusters more than 2.sup.(k-i-1) are selected in order from the
oldest track in the WC and added to the flush candidates until the
number of tracks reaches 2.sup.i.
[0124] When track flush is performed under the condition (i) and
the track is flushed to the FS 12, a track satisfying the condition
that an amount of data to be flushed does not exceed 50% of a track
size is selected in order of LRUs among the tracks in the WC 21 and
clusters of the track are added to the flush candidates until the
number of clusters to be flushed reaches 2.sup.k. In other words,
clusters are extracted from tracks having 2.sup.(k-i-1) or less
valid clusters by tracing the tracks in the WC in order from the
oldest one and, when the number of valid clusters reaches 2.sup.k,
the clusters are flushed to the FSIB 12a in logical block units.
However, when 2.sup.k valid clusters are not found, clusters are
flushed to the FSIB 12a in logical page units. A threshold of the
number of valid clusters for determining whether the flush to the
FS 12 is performed in logical block units or logical page units is
not limited to a value for one logical block, i.e., 2.sup.k and can
be a value slightly smaller than the value for one logical
block.
[0125] In a Cache Flush request from the ATA-command processing
unit 121, all contents of the WC 21 are flushed to the FS 12 or the
MS 11 under conditions same as the above (when an amount of data to
be flushed exceeds 50% of a track size, the data is flushed to the
MS 11 and, when the amount of data does not exceed 50%, the data is
flushed to the FS 12).
Pre-Stage Storage Area (FS) 12
[0126] The FS 12 is explained. The FS 12 adapts an FIFO structure
of logical block units in which data is managed in cluster units.
The FS 12 is a buffer for regarding that data passing through the
FS 12 has an update frequency higher than that of the IS 13 at the
post stage. In other words, in the FIFO structure of the FS 12, a
valid cluster (a latest cluster) passing through the FIFO is
invalidated when rewriting in the same address from the host is
performed. Therefore, the cluster passing through the FS 12 can be
regarded as having an update frequency higher than that of a
cluster flushed from the FS 12 to the IS 13 or the MS 11.
[0127] By providing the FS 12, likelihood of mixing of data with a
high update frequency in compaction processing in the IS 13 at the
post stage is reduced. When the number of valid clusters of a
logical block is reduced to 0 by the invalidation, the logical
block is released and allocated to the free block FB. When the
logical block in the FS 12 is invalidated, a new free block FB is
acquired and allocated to the FS 12.
[0128] When cluster flush from the WC 21 to the FS 12 is performed,
the cluster is written in a logical block allocated to the FSIB
12a. When logical blocks, for which writing of all logical pages is
completed, are present in the FSIB 12a, the logical blocks are
moved from the FSIB 12a to the FS 12 by CIB processing explained
later. In moving the logical blocks from the FSIB 12a to the FS 12,
when the number of logical blocks of the FS 12 exceeds a
predetermined upper limit value allowed for the FS 12, an oldest
logical block is flushed from the FS 12 to the IS 13 or the MS 11.
For example, a track with a ratio of valid clusters in the track
equal to or larger than 50% is written in the MS 11 (the TFS 11b)
and a logical block in which the valid cluster remains is moved to
the IS 13.
[0129] As the data movement between components in the NAND memory
10, there are two ways, i.e., Move and Copy. Move is a method of
simply performing relocation of a pointer of a management table
explained later and not performing actual rewriting of data. Copy
is a method of actually rewriting data stored in one component to
the other component in page units, track units, or block units.
Intermediate Stage Storage Area (IS) 13
[0130] The IS 13 is explained. In the IS 13, management of data is
performed in cluster units in the same manner as the FS 12. Data
stored in the IS 13 can be regarded as data with a low update
frequency. When movement (Move) of a logical block from the FS 12
to the IS 13, i.e., flush of the logical block from the FS 12 is
performed, a logical block as an flush object, which is previously
a management object of the FS 12, is changed to a management object
of the IS 13 by the relocation of the pointer. According to the
movement of the logical block from the FS 12 to the IS 13, when the
number of blocks of the IS 13 exceeds a predetermined upper limit
value allowed for the IS 13, i.e., when the number of writable free
blocks FB in the IS decreases to be smaller than a threshold, data
flush from the IS 13 to the MS 11 and compaction processing are
executed. The number of blocks of the IS 13 is returned to a
specified value.
[0131] The IS 13 executes flush processing and compaction
processing explained below using the number of valid clusters in a
track.
[0132] Tracks are sorted in order of the number of valid
clusters.times.valid cluster coefficient (the number weighted
according to whether a track is present in a logical block in which
an invalid track is present in the MS 11; the number is larger when
the invalid track is present than when the invalid track is not
present). 2.sup.i+1 tracks (for two logical blocks) with a large
value of a product are collected, increased to be natural number
times as large as a logical block size, and flushed to the MSIB
11a.
[0133] When a total number of valid clusters of two logical blocks
with a smallest number of valid clusters is, for example, equal to
or larger than 2.sup.k (for one logical block), which is a
predetermined set value, the step explained above is repeated (to
perform the step until a free block FB can be created from two
logical blocks in the IS).
[0134] 2.sup.k clusters are collected in order from logical blocks
with a smallest number of valid clusters and compaction is
performed in the IS.
[0135] Here, the two logical blocks with the smallest number of
valid clusters are selected. However, the number is not limited to
two and only has to be a number equal to or larger than two. The
predetermined set value only has to be equal to or smaller than the
number of clusters that can be stored in the number of logical
blocks smaller than the number of selected logical blocks by
one.
Main Storage Area (MS) 11
[0136] The MS 11 is explained. In the MS 11, management of data is
performed in track units. Data stored in the MS 11 can be regarded
as having a low update frequency. When Copy or Move of track from
the WC 21, the FS 12, or the IS 13 to the MS 11 is performed, the
track is written in a logical block allocated to the MSIB 11a. On
the other hand, when only data (clusters) in a part of the track is
written from the FS 12, the IS 13 or the like, passive merge
explained later for merging existing track in the MS 11 and new
data to create new track and, then, writing the created track in
the MSIB 11a is performed. When invalid tracks are accumulated in
the MS 11 and the number of logical blocks allocated to the MS 11
exceeds the upper limit of the number of blocks allowed for the MS
11, compaction processing is performed to create a free block
FB.
[0137] As the compaction processing of the MS 11, for example, a
method explained below with attention paid to only the number of
valid tracks in a logical block is carried out.
[0138] Logical blocks are selected from one with a smallest number
of valid tracks until a free block FB can be created by combining
invalid tracks.
[0139] Compaction is executed while passive merge for integrating
tracks stored in the selected logical blocks with data in the WC
21, the FS 12, or the IS 13 is performed.
[0140] A logical block in which 2.sup.i tracks can be integrated is
output to the TFS 11b (2.sup.i track MS compaction) and tracks
smaller in number than 2.sup.i are output to the MSIB 11a (less
than 2.sup.i track compaction) to create a larger number of free
blocks FB.
[0141] The TFS 11b adapts an FIFO structure of logical block units
in which data is managed in track units. The TFS 11b is a buffer
for regarding that data passing through the TFS 11b has an update
frequency higher than that of the MS 11 at the post stage. In other
words, in the FIFO structure of the TFS 11b, a valid track (a
latest track) passing through the FIFO is invalidated when
rewriting in the same address from the host is performed.
Therefore, a track passing through the TFS 11b can be regarded as
having an update frequency higher than that of a track flushed from
the TFS 11b to the MS 11.
[0142] FIG. 8 is a diagram of a management table for the data
managing unit 120 to control and manage the respective components
shown in FIGS. 5 and 6. The data managing unit 120 has, as
explained above, the function of bridging the ATA-command
processing unit 121 and the NAND memory 10 and includes a
DRAM-layer managing unit 120a that performs management of data
stored in the DRAM 20, a logical-NAND-layer managing unit 120b that
performs management of data stored in the NAND memory 10, and a
physical-NAND-layer managing unit 120c that manages the NAND memory
10 as a physical storage device. An RC cluster management table 23,
a WC track management table 24, and a WC cluster management table
25 are controlled by the DRAM-layer managing unit 120a. A track
management table 30, an FS/IS management table 40, an MS logical
block management table 35, an FS/IS logical block management table
42, and an intra-FS/IS cluster management table 44 are managed by
the logical-NAND-layer managing unit 120b. A logical-to-physical
translation table 50 is managed by the physical-NAND-layer managing
unit 120c.
[0143] The RC 22 is managed by the RC cluster management table 23,
which is a reverse lookup table. In the reverse lookup table, from
a position of a storage device, a logical address stored in the
position can be searched. The WC 21 is managed by the WC cluster
management table 25, which is a reverse lookup table, and the WC
track management table 24, which is a forward lookup table. In the
forward lookup table, from a logical address, a position of a
storage device in which data corresponding to the logical address
is present can be searched.
[0144] Logical addresses of the FS 12 (the FSIB 12a), the IS 13,
and the MS 11 (the TFS 11b and the MSIB 11a) in the NAND memory 10
are managed by the track management table 30, the FS/IS management
table 40, the MS logical block management table 35, the FS/IS
logical block management table 42, and the intra-FS/IS cluster
management table 44. In the FS 12 (the FSIB 12a), the IS 13, and
the MS 11 (the TFS 11b and MSIB 11a) in the NAND memory 10,
conversion of a logical address and a physical address is performed
of the logical-to-physical translation table 50. These management
tables are stored in an area on the NAND memory 10 and read onto
the DRAM 20 from the NAND memory 10 during initialization of the
SSD 100.
RC Cluster Management Table 23 (Reverse Lookup)
[0145] The RC cluster management table 23 is explained with
reference to FIG. 9. As explained above, the RC 22 is managed in
the n-way set associative system indexed by logical cluster address
LSB (k-i) bits. The RC cluster management table 23 is a table for
managing tags of respective entries of the RC (the cluster
size.times.m-line.times.n-way) 22. Each of the tags includes a
state flag 23a including a plurality of bits and a logical track
address 23b. The state flag 23a includes, besides a valid bit
indicating whether the entry may be used (valid/invalid), for
example, a bit indicating whether the entry is on a wait for
readout from the NAND memory 10 and a bit indicating whether the
entry is on a wait for readout to the ATA-command processing unit
121. The RC cluster management table 23 functions as a reverse
lookup table for searching for a logical track address coinciding
with LBA from a tag storage position on the DRAM 20.
WC Cluster Management Table 25 (Reverse Lookup)
[0146] The WC cluster management table 25 is explained with
reference to FIG. 10. As explained above, the WC 21 is managed in
the n-way set associative system indexed by logical cluster address
LSB (k-i) bits. The WC cluster management table 25 is a table for
managing tags of respective entries of the WC (the cluster
size.times.m-line.times.n-way) 21. Each of the tags includes a
state flag 25a of a plurality of bits, a sector position bitmap
25b, and a logical track address 25c.
[0147] The state flag 25a includes, besides a valid bit indicating
whether the entry may be used (valid/invalid), for example, a bit
indicating whether the entry is on a wait for flush to the NAND
memory 10 and a bit indicating whether the entry is on a wait for
writing from the ATA-command processing unit 121. The sector
position bitmap 25b indicates which of 2.sup.(l-k) sectors included
in one cluster stores valid data by expanding the sectors into
2.sup.(l-k) bits. With the sector position bitmap 25b, management
in sector units same as the LBA can be performed in the WC 21. The
WC cluster management table 25 functions as a reverse lookup table
for searching for a logical track address coinciding with the LBA
from a tag storage position on the DRAM 20.
WC Track Management Table 24 (Forward Lookup)
[0148] The WC track management table 24 is explained with reference
to FIG. 11. The WC track management table 24 is a table for
managing information in which clusters stored on the WC 21 are
collected in track units and represents the order (LRU) of
registration in the WC 21 among the tracks using the linked list
structure having an FIFO-like function. The LRU can be represented
by the order updated last in the WC 21. An entry of each list
includes a logical track address 24a, the number of valid clusters
24b in the WC 21 included in the logical track address, a way-line
bitmap 24c, and a next pointer 24d indicating a pointer to the next
entry. The WC track management table 24 functions as a forward
lookup table because required information is obtained from the
logical track address 24a.
[0149] The way-line bitmap 24c is map information indicating in
which of m.times.n entries in the WC 21 a valid cluster included in
the logical track address in the WC 21 is stored. The Valid bit is
"1" in an entry in which the valid cluster is stored. The way-line
bitmap 24c includes, for example, (one bit (valid)+log.sub.2 n bits
(n-way)).times.m bits (m-line). The WC track management table 24
has the linked list structure. Only information concerning the
logical track address present in the WC 21 is entered.
Track Management Table 30 (Forward Lookup)
[0150] The track management table 30 is explained with reference to
FIG. 12. The track management table 30 is a table for managing a
logical data position on the MS 11 in logical track address units.
When data is stored in the FS 12 or the IS 13 in cluster units, the
track management table 30 stores basic information concerning the
data and a pointer to detailed information. The track management
table 30 is configured in an array format having a logical track
address 30a as an index. Each entry having the logical track
address 30a as an index includes information such as a cluster
bitmap 30b, a logical block ID 30c+an intra-logical block track
position 30d, a cluster table pointer 30e, the number of FS
clusters 30f, and the number of IS clusters 30g. The track
management table 30 functions as a forward lookup table because,
using a logical track address as an index, required information
such as a logical block ID (corresponding to a storage device
position) in which track corresponding to the logical track address
is stored.
[0151] The cluster bitmap 30b is a bitmap obtained by dividing
2.sup.(k-i) clusters belonging to one logical track address range
into, for example, eight in ascending order of logical cluster
addresses. Each of eight bits indicates whether clusters
corresponding to 2.sup.(k-i-3) cluster addresses are present in the
MS 11 or present in the FS 12 or the IS 13. When the bit is "0",
this indicates that the clusters as search objects are surely
present in the MS 11. When the bit is "1", this indicates that the
clusters are likely to be present in the FS 12 or the IS 13.
[0152] The logical block ID 30c is information for identifying a
logical block ID in which track corresponding to the logical track
address is stored. The intra-logical block track position 30d
indicates a storage position of a track corresponding to the
logical track address (30a) in the logical block designated by the
logical block ID 30c. Because one logical block includes maximum
2.sup.i valid tracks, the intra-logical block track position 30d
identifies 2.sup.i track positions using i bits.
[0153] The cluster table pointer 30e is a pointer to a top entry of
each list of the FS/IS management table 40 having the linked list
structure. In the search through the cluster bitmap 30b, when it is
indicated that the cluster is likely to be present in the FS 12 or
the IS 13, search through the FS/IS management table 40 is executed
by using the cluster table pointer 30e. The number of FS clusters
30f indicates the number of valid clusters present in the FS 12.
The number of IS clusters 30g indicates the number of valid
clusters present in the IS 13.
FS/IS Management Table 40 (Forward Lookup)
[0154] The FS/IS management table 40 is explained with reference to
FIG. 13. The FS/IS management table 40 is a table for managing a
position of data stored in the FS 12 (including the FSIB 12a) or
the IS 13 in logical cluster addresses. As shown in FIG. 13, the
FS/IS management table 40 is formed in an independent linked list
format for each logical track address. As explained above, a
pointer to a top entry of each list is stored in a field of the
cluster table pointer 30e of the track management table 30. In FIG.
13, linked lists for two logical track addresses are shown. Each
entry includes a logical cluster address 40a, a logical block ID
40b, an intra-logical block cluster position 40c, an FS/IS block ID
40d, and a next pointer 40e. The FS/IS management table 40
functions as a forward lookup table because required information
such as the logical block ID 40b and the intra-logical block
cluster position 40c (corresponding to a storage device position)
in which cluster corresponding to the logical cluster address 40a
is stored is obtained from the logical cluster address 40a.
[0155] The logical block ID 40b is information for identifying a
logical block ID in which cluster corresponding to the logical
cluster address 40a is stored. The intra-logical block cluster
position 40c indicates a storage position of a cluster
corresponding to the logical cluster address 40a in a logical block
designated by the logical block ID 40b. Because one logical block
includes maximum 2.sup.k valid clusters, the intra-logical block
cluster position 40c identifies 2.sup.k positions using k bits. An
FS/IS block ID, which is an index of the FS/IS logical block
management table 42 explained later, is registered in the FS/IS
block ID 40d. The FS/IS block ID 40d is information for identifying
a logical block belonging to the FS 12 or the IS 13. The FS/IS
block ID 40d in the FS/IS management table 40 is registered for
link to the FS/IS logical block management table 42 explained
later. The next pointer 40e indicates a pointer to the next entry
in the same list linked for each logical track address.
MS Logical Block Management Table 35 (Reverse Lookup)
[0156] The MS logical block management table 35 is explained with
reference to FIG. 14. The MS logical block management table 35 is a
table for unitarily managing information concerning a logical block
used in the MS 11 (e.g., which track is stored and whether a track
position is additionally recordable). In the MS logical block
management table 35, information concerning logical blocks
belonging to the FS 12 (including the FSIB 12) and the IS 13 is
also registered. The MS logical block management table 35 is formed
in an array format having a logical block ID 35a as an index. The
number of entries can be 32 K entries at the maximum in the case of
the 128 GB NAND memory 10. Each of the entries includes a track
management pointer 35b for 2.sup.i tracks, the number of valid
tracks 35c, a writable top track 35d, and a valid flag 35e. The MS
logical block management table 35 functions as a reverse lookup
table because required information such as a logical track address
stored in the logical block is obtained from the logical block ID
35a corresponding to a storage device position.
[0157] The track management pointer 35b stores a logical track
address corresponding to each of 2.sup.i track positions in the
logical block designated by the logical block ID 35a. It is
possible to search through the track management table 30 having the
logical track address as an index using the logical track address.
The number of valid tracks 35c indicates the number of valid tracks
(maximum 2.sup.i) among tracks stored in the logical block
designated by the logical block ID 35a. The writable top track
position 35d indicates a top position (0 to 2.sup.i-1, 2.sup.i when
additional recording is finished) additionally recordable when the
logical block designated by the logical block ID 35a is a block
being additionally recorded. The valid flag 35e is "1" when the
logical block entry is managed as the MS 11 (including the MSIB
11a). Here, "additional recording" means that writing cluster or
track, in appending manner, to empty logical pages in a logical
block.
FS/IS Logical Block Management Table 42 (Reverse Lookup)
[0158] The FS/IS logical block management table 42 is explained
with reference to FIG. 15. The FS/IS logical block management table
42 is formed in an array format having an FS/IS block ID 42a as an
index. The FS/IS logical block management table 42 is a table for
managing information concerning a logical block used as the FS 12
or the IS 13 (correspondence to a logical block ID, an index to the
intra-FS/IS cluster management table 44, whether the logical block
is additionally recordable, etc.). The FS/IS logical block
management table 42 is accessed by mainly using the FS/IS block ID
40d in the FS/IS management table 40. Each entry includes a logical
block ID 42b, an intra-block cluster table 42c, the number of valid
clusters 42d, a writable top page 42e, and a valid flag 42f. The MS
logical block management table 35 functions as a reverse lookup
table because required information such as cluster stored in the
logical block is obtained from the FS/IS block ID 42 corresponding
to a storage device position.
[0159] Logical block IDs corresponding to logical blocks belonging
to the FS 12 (including the FSIB 12) and the IS 13 among logical
blocks registered in the MS logical block management table 35 are
registered in the logical block ID 42b. An index to the intra-FS/IS
cluster management table 44 explained later indicating a logical
cluster designated by which logical cluster address is registered
in each cluster position in a logical block is registered in the
intra-block cluster table 42c. The number of valid clusters 42d
indicates the number of (maximum 2.sup.k) valid clusters among
clusters stored in the logical block designated by the FS/IS block
ID 42a. The writable top page position 42e indicates a top page
position (0 to 2.sup.j-1, 2.sup.i when additional recording is
finished) additionally recordable when the logical block designated
by the FS/IS block ID 42a is a block being additionally recorded.
The valid flag 42f is "1" when the logical block entry is managed
as the FS 12 (including the FSIB 12) or the IS 13.
Intra-FS/IS Cluster Management Table 44 (Reverse Lookup)
[0160] The intra-FS/IS cluster management table 44 is explained
with reference to FIG. 16. The intra-FS/IS cluster management table
44 is a table indicating which cluster is recorded in each cluster
position in a logical block used as the FS 12 or the IS 13. The
intra-FS/IS cluster management table 44 has 2.sup.j
pages.times.2.sup.(k-j) clusters=2.sup.k entries per one logical
block. Information corresponding to 0th to 2.sup.k-1th cluster
positions among cluster positions in the logical block is arranged
in continuous areas. Tables including the 2.sup.k pieces of
information are stored by the number equivalent to the number of
logical blocks (P) belonging to the FS 12 and the IS 13. The
intra-block cluster table 42c of the FS/IS logical block management
table 42 is positional information (a pointer) for the P tables. A
position of each entry 44a arranged in the continuous areas
indicates a cluster position in one logical block. As content of
the entry 44a, a pointer to a list including a logical cluster
address managed by the FS/IS management table 40 is registered such
that it is possible to identify which cluster is stored in the
cluster position. In other words, the entry 44a does not indicate
the top of a linked list. A pointer to one list including the
logical cluster address in the linked list is registered in the
entry 44a.
Logical-to-Physical Translation Table 50 (Forward Lookup)
[0161] The logical-to-physical translation table 50 is explained
with reference to FIG. 17. The logical-to-physical translation
table 50 is formed in an array format having a logical block ID 50a
as an index. The number of entries can be maximum 32 K entries in
the case of the 128 GB NAND memory 10. The logical-to-physical
translation table 50 is a table for managing information concerning
conversion between a logical block ID and a physical block ID and
the life. Each of the entries includes a physical block address
50b, the number of times of erasing 50c, and the number of times of
readout 50d. The logical-to-physical translation table 50 functions
as a forward lookup table because required information such as a
physical block ID (a physical block address) is obtained from a
logical block ID.
[0162] The physical block address 50b indicates eight physical
block IDs (physical block addresses) belonging to one logical block
ID 50a. The number of times of erasing 50c indicates the number of
times of erasing of the logical block ID. A bad block (BB) is
managed in physical block (512 KB) units. However, the number of
times of erasing is managed in one logical block (4 MB) units in
the 32-bit double speed mode. The number of times of readout 50d
indicates the number of times of readout of the logical block ID.
The number of times of erasing 50c can be used in, for example,
wear leveling processing for leveling the number of times of
rewriting of a NAND-type flash memory. The number of times of
readout 50d can be used in refresh processing for rewriting data
stored in a physical block having deteriorated retention
properties.
[0163] An example of the wear leveling processing is described in
the International Application No. PCT/JP2008/066508 and No.
PCT/JP2008/066507. An example of the refresh processing is
described in the International Application No. PCT/JP2008/067597,
the entire contents of which are incorporated herein by
reference.
[0164] The management tables shown in FIG. 8 are collated by
management object as explained below.
[0165] RC management: The RC cluster management table 23
[0166] WC management: The WC cluster management table 25 and the WC
track management table 24
[0167] MS management: The track management table 30 and the MS
logical block management table 35
[0168] FS/IS management: The track management table 30, the FS/IS
management table 40, the MS logical block management table 35, the
FS/IS logical block management table 42, and the intra-FS/IS
cluster management table 44
[0169] The structure of an MS area including the MS 11, the MSIB
11a, and the TFS 11b is managed in an MS structure management table
(not shown). Specifically, logical blocks and the like allocated to
the MS 11, the MSIB 11a, and the TFS 11b are managed. The structure
of an FS/IS area including the FS 12, the FSIB 12a, and the IS 13
is managed in an FS/IS structure management table (not shown).
Specifically, logical blocks and the like allocated to the FS 12,
the FSIB 12a, and the IS 13 are managed.
Read Processing
[0170] Read processing is explained with reference to a flowchart
shown in FIG. 18. When a Read command, LBA as a readout address,
and a readout size are input from the ATA-command processing unit
121, the data managing unit 120 searches through the RC cluster
management table 23 shown in FIG. 9 and the WC cluster management
table 25 shown in FIG. 10 (step S100). Specifically, the data
managing unit 120 selects lines corresponding to LSB (k-i) bits
(see FIG. 7) of a logical cluster address of the LBA from the RC
cluster management table 23 and the WC cluster management table 25
and compares logical track addresses 23b and 25c entered in each
way of the selected lines with a logical track address of the LBA
(step S110). When a way such that a logical track address entered
in itself coincides with a logical track address of LBA is present,
the data managing unit 120 regards this as cache hit. The data
managing unit 120 reads out data of the WC 21 or the RC 22
corresponding to the hit line and way of the RC cluster management
table 23 or the WC cluster management table 25 and sends the data
to the ATA-command processing unit 121 (step S115).
[0171] When there is no hit in the RC 22 or the WC 21 (step S110),
the data managing unit 120 searches in which part of the NAND
memory 10 a cluster as a search object is stored. First, the data
managing unit 120 searches through the track management table 30
shown in FIG. 12 (step S120). The track management table 30 is
indexed by the logical track address 30a. Therefore, the data
managing unit 120 checks only entries of the logical track address
30a coinciding with the logical track address designated by the
LBA.
[0172] The data managing unit 120 selects a corresponding bit from
the cluster bitmap 30b based on a logical cluster address of the
LBA desired to be checked. When the corresponding bit indicates
"0", this means that latest data of the cluster is surely present
the MS (step S130). In this case, the data managing unit 120
obtains logical block ID and a track position in which the track is
present from the logical block ID 30c and the intra-logical block
track position 30d in the same entry of the logical track address
30a. The data managing unit 120 calculates an offset from the track
position using LSB (k-i) bits of the logical cluster address of the
LBA. Consequently, the data managing unit 120 can calculate
position where cluster corresponding to the logical cluster address
in the NAND memory 10 is stored. Specifically, the
logical-NAND-layer managing unit 120b gives the logical block ID
30c and the intra-logical block position 30d acquired from the
track management table 30 as explained above and the LSB (k-i) bits
of the logical cluster address of the LBA to the
physical-NAND-layer managing unit 120c.
[0173] The physical-NAND-layer managing unit 120c acquires a
physical block address (a physical block ID) corresponding to the
logical block ID 30c from the logical-to-physical translation table
50 shown in FIG. 17 having the logical block ID as an index (step
S160). The data managing unit 120 calculates a track position (a
track top position) in the acquired physical block ID from the
intra-logical block track position 30d and further calculates, from
the LSB (k-i) bits of the logical cluster address of the LBA, an
offset from the calculated track top position in the physical block
ID. Consequently, the data managing unit 120 can acquire cluster in
the physical block. The data managing unit 120 sends the cluster
acquired from the MS 11 of the NAND memory 10 to the ATA-command
processing unit 121 via the RC 22 (step S180).
[0174] On the other hand, when the corresponding bit indicates "1"
in the search through the cluster bitmap 30b based on the logical
cluster address of the LBA, it is likely that the cluster is stored
in the FS 12 or the IS 13 (step S130). In this case, the data
managing unit 120 extracts an entry of the cluster table pointer
30e among relevant entries of the logical track address 30a in the
track management table 30 and sequentially searches through linked
lists corresponding to a relevant logical track address of the
FS/IS management table 40 using this pointer (step S140).
Specifically, the data managing unit 120 searches for an entry of
the logical cluster address 40a coinciding with the logical cluster
address of the LBA in the linked list of the relevant logical track
address. When the coinciding entry of the logical cluster address
40a is present (step S150), the data managing unit 120 acquires the
logical block ID 40b and the intra-logical block cluster position
40c in the coinciding list. In the same manner as explained above,
the data managing unit 120 acquires the cluster in the physical
block using the logical-to-physical translation table 50 (steps
S160 and S180). Specifically, the data managing unit 120 acquires
physical block addresses (physical block IDs) corresponding to the
acquired logical block ID from the logical-to-physical translation
table 50 (step S160) and calculates a cluster position of the
acquired physical block ID from an intra-logical block cluster
position acquired from an entry of the intra-logical block cluster
position 40c. Consequently, the data managing unit 120 can acquire
the cluster in the physical block. The data managing unit 120 sends
the cluster acquired from the FS 12 or the IS 13 of the NAND memory
10 to the ATA-command processing unit 121 via the RC 22 (step
S180).
[0175] When the cluster as the search object is not present in the
search through the FS/IS management table 40 (step S150), the data
managing unit 120 searches through the entries of the track
management table 30 again and decides a position on the MS 11 (step
S170).
Write Processing
[0176] Write processing is explained with reference to a flowchart
shown in FIG. 19. Data written by a Write command is always once
stored on the WC 21. Thereafter, the data is written in the NAND
memory 10 according to conditions. In the write processing, it is
likely that flush processing and compaction processing are
performed. In this embodiment, the write processing is roughly
divided into two stages of write cache flash processing
(hereinafter, WCF processing) and clean input buffer processing
(hereinafter, CIB processing). Steps S300 to S320 indicate
processing from a Write request from the ATA-command processing
unit 121 to the WCF processing. Step S330 to the last step indicate
the CIB processing.
[0177] The WCF processing is processing for copying data in the WC
21 to the NAND memory 10 (the FSIB 12a of the FS 12 or the MSIB 11a
of the MS 11). A Write request or a Cache Flush request alone from
the ATA-command processing unit 121 can be completed only by this
processing. This makes it possible to limit a delay in the started
processing of the Write request of the ATA-command processing unit
121 to, at the maximum, time for writing in the NAND memory 10
equivalent to a capacity of the WC 21.
[0178] The CIB processing includes processing for moving the data
in the FSIB 12a written by the WCF processing to the FS 12 and
processing for moving the data in the MSIB 11a written by the WCF
processing to the MS 11. When the CIB processing is started, it is
likely that data movement among the components (the FS 12, the IS
13, the MS 11, etc.) in the NAND memory and compaction processing
are performed in a chain-reacting manner. Time required for the
overall processing substantially changes according to a state.
WCF Processing
[0179] First, details of the WCF processing are explained. When a
Write command, LBA as a writing address, and a writing size is
input from the ATA-command processing unit 121, the DRAM-layer
managing unit 120a searches through the WC cluster management table
25 shown in FIG. 10 (steps S300 and S305). A state of the WC 21 is
defined by the state flag 25a (e.g., 3 bits) of the WC cluster
management table 25 shown in FIG. 10. Most typically, a state of
the state flag 25a transitions in the order of invalid
(usable).fwdarw.a wait for writing from an ATA.fwdarw.valid
(unusable).fwdarw.a wait for flush to an NAND.fwdarw.invalid
(usable). First, a line at a writing destination is determined from
logical cluster address LSB (k-i) bits of the LBA and n ways of the
determined line are searched. When the logical track address 25c
same as that of the input LBA is stored in the n ways of the
determined lines (step S305), the DRAM-layer managing unit 120a
secures this entry as an entry for writing cluster because the
entry is to be overwritten (valid (unusable).fwdarw.a wait for
writing from an ATA).
[0180] The DRAM-layer managing unit 120a notifies the ATA-command
processing unit 121 of a DRAM address corresponding to the entry.
When writing by the ATA-command processing unit 121 is finished,
the data managing unit 120 changes the state flag 25a of the entry
to valid (unusable) and registers required data in spaces of the
sector position bitmap 25b and the logical track address 25c. The
data managing unit 120 updates the WC track management table 24.
Specifically, when an LBA address same as the logical track address
24a already registered in the lists of the WC track management
table 24 is input, the data managing unit 120 updates the number of
WC clusters 24b and the way-line bitmap 24c of a relevant list and
changes the next pointer 24d such that the list becomes a latest
list. When an LBA address different from the logical track address
24a registered in the lists of the WC track management table 24 is
input, the data managing unit 120 creates a new list having the
entries of the logical track address 24a, the number of WC clusters
24b, the way-line bitmap 24c, and the next pointer 24d and
registers the list as a latest list. The data managing unit 120
performs the table update explained above to complete the write
processing (step S320).
[0181] On the other hand, when the logical track address 25c same
as that of the input LBA is not stored in the n ways of the
determined line, the data managing unit 120 judges whether flush to
the NAND memory 10 is necessary (step S305). First, the data
managing unit 120 judges whether a writable way in the determined
line is a last nth way. The writable way is a way having the state
flag 25a of invalid (usable) or a way having the state flag 25a of
valid (unusable) and a wait for flush to a NAND. When the state
flag 25a is a wait for flush to a NAND, this means that flush is
started and an entry is a wait for the finish of the flush. When
the writable way is not the last nth way and the writable way is a
way having the state flag 25a of invalid (usable), the data
managing unit 120 secures this entry as an entry for cluster
writing (invalid (usable).fwdarw.a wait for writing from an ATA).
The data managing unit 120 notifies the ATA-command processing unit
121 of a DRAM address corresponding to the entry and causes the
ATA-command processing unit 121 to execute writing. In the same
manner as explained above, the data managing unit 120 updates the
WC cluster management table 25 and the WC track management table 24
(step S320).
[0182] When the writable way is not the last nth way and when the
writable way is the way having the state flag 25a of valid
(unusable) and a wait for flush to a NAND, the data managing unit
120 secures this entry as an entry for writing cluster (valid
(unusable) and a wait for flush to a NAND.fwdarw.valid (unusable)
and a wait for flush from a NAND and a wait for writing from an
ATA). When the flush is finished, the data managing unit 120
changes the state flag 25a to a wait for writing from an ATA,
notifies the ATA-command processing unit 121 of a DRAM address
corresponding to the entry, and causes the ATA-command processing
unit 121 to execute writing. In the same manner as explained above,
the data managing unit 120 updates the WC cluster management table
25 and the WC track management table 24 (step S320).
[0183] The processing explained above is performed when flush
processing does not have to be triggered when a writing request
from the ATA-command processing unit 121 is input. On the other
hand, processing explained below is performed when flush processing
is triggered after a writing request is input. At step S305, when
the writable way in the determined line is the last nth way, the
data managing unit 120 selects track to be flushed, i.e., an entry
in the WC 21 based on the condition explained in (i) of the method
of determining data to be flushed from the WC 21 to the NAND memory
10, i.e.,
[0184] (i) when a writable way determined by a tag is a last (in
this embodiment, nth) free way, i.e., when the last free way is to
be used, track updated earliest based on an LRU among track
registered in the line is decided to be flushed.
[0185] When that track to be flushed is determined according to the
policy explained above, as explained above, if all cluster in the
WC 21 included in an identical logical track address are to be
flushed and an amount of cluster to be flushed exceeds 50% of a
track size, i.e., if the number of valid cluster in the WC is equal
to or larger than 2.sup.(k-i-1) in the track decided to be flushed,
the DRAM-layer managing unit 120a performs flush to the MSIB 11a
(step S310). If the amount of cluster does not exceeds 50% of the
track size, i.e., the number of valid cluster in the WC is smaller
than 2.sup.(k-i-1) in the track decided to be flushed, the
DRAM-layer managing unit 120a performs flush to the FSIB 12a (step
S315). Details of the flush from the WC 21 to the MSIB 11a and the
flush from the WC 21 to the FSIB 12a are explained later. The state
flag 25a of the selected flush entry is transitioned from Valid
(unusable) to a wait for flush to the NAND memory 10.
[0186] This judgment on a flush destination is executed by using
the WC track management table 24. An entry of the number of WC
clusters 24 indicating the number of valid clusters is registered
in the WC track management table 24 for each logical track address.
The data managing unit 120 determines which of the FSIB 12a and the
MSIB 11a should be set as a destination of flush from the WC 21
referring to the entry of the number of WC clusters 24b. All
clusters belonging to the logical track address are registered in a
bitmap format in the way-line bitmap 24c. Therefore, in performing
flush, the data managing unit 120 can easily learn, referring to
the way-line bitmap 24c, a storage position in the WC 21 of each of
the cluster that should be flushed.
[0187] During the write processing or after the write processing,
the data managing unit 120 also execute the flush processing to the
NAND memory 10 in the same manner when the following condition is
satisfied:
(ii) the number of tracks registered in the WC 21 exceeds a
predetermined number.
WC.fwdarw.MSIB (Copy)
[0188] When flush from the WC 21 to the MSIB 11a is performed
according to the judgment based on the number of valid clusters
(the number of valid clusters is equal to or larger than
2.sup.(k-i-1)), the data managing unit 120 executes a procedure
explained below as explained above (step S310).
[0189] 1. Referring to the WC cluster management table 25 and
referring to the sector position bitmaps 25b in tags corresponding
to cluster to be flushed, when all the sector position bitmaps 25b
are not "1", the data managing unit 120 performs intra-track sector
padding explained later for merging with sector not present in the
WC 21 by reading out the missing sector included in the identical
logical track address from the NAND memory 10.
[0190] 2. When the number of tracks decided to be flushed is less
than 2.sup.i, the data managing unit 120 adds tracks decided to be
flushed having 2.sup.(k-i-1) or more valid clusters until the
number of tracks decided to be flushed reaches 2.sup.i from the
oldest one in the WC 21.
[0191] 3. When there are 2.sup.i or more tracks to be copied, the
data managing unit 120 performs writing in the MSIB 11a in logical
block units with each 2.sup.i tracks as a set.
[0192] 4. The data managing unit 120 writes the tracks that cannot
form a set of 2.sup.i tracks in the MSIB 11a in track units.
[0193] 5. The data managing unit 120 invalidates clusters and
tracks belonging to the copied tracks among those already present
on the FS, the IS, and the MS after the Copy is finished.
[0194] Update processing for the respective management tables
involved in the Copy processing from the WC 21 to the MSIB 11a is
explained. The data managing unit 120 sets the state flag 25a in
entries corresponding to all clusters in the WC 21 belonging to a
flushed track in the WC cluster management table 25 Invalid.
Thereafter, writing in these entries is possible. Concerning a list
corresponding to the flushed track in the WC track management table
24, the data managing unit 120 changes or deletes, for example, the
next pointer 24d of an immediately preceding list and invalidates
the list.
[0195] On the other hand, when track flush from the WC 21 to the
MSIB 11a is performed, the data managing unit 120 updates the track
management table 30 and the MS logical block management table 35
according to the track flush. First, the data managing unit 120
searches for the logical track address 30a as an index of the track
management table 30 to judge whether the logical track address 30a
corresponding to the flushed track is already registered. When the
logical track address 30a is already registered, the data managing
unit 120 updates fields of the cluster bitmap 30b (because the
track is flushed to the MS 11 side, all relevant bits are set to
"0") of the index and the logical block ID 30c+the intra-logical
block track position 30d. When the logical track address 30a
corresponding to the flushed track is not registered, the data
managing unit 120 registers the cluster bitmap 30b and the logical
block ID 30c+the intra-logical block track position 30d in an entry
of the relevant logical track address 30a. The data managing unit
120 updates, according to the change of the track management table
30, entries of the logical block ID 35a, the track management
pointer 35b, the number of valid tracks 35c, the writable top track
35d, and the like in the MS logical block management table 35 when
necessary.
[0196] When track writing is performed from other areas (the FS 12
and the IS 13) or the like to the MS 11 or when intra-MS track
writing by compaction processing in the MS 11 is performed, valid
clusters in the WC 21 included in the logical track address as a
writing object may be simultaneously written in the MS 11. Such
passive merge may be present as writing from the WC 21 to the MS
11. When such passive merge is performed, the clusters are deleted
from the WC 21 (invalidated).
WC.fwdarw.FSIB (Copy)
[0197] When flush from the WC 21 to the FSIB 12a is performed
according to the judgment based on the number of valid clusters
(the number of valid clusters is equal to or larger than
2.sup.(k-i-1)), the data managing unit 120 executes a procedure
explained below.
[0198] 1. Referring to the sector position bitmaps 25b in tags
corresponding to clusters to be flushed, when all the sector
position bitmaps 25b are not "1", the data managing unit 120
performs intra-cluster sector padding for merging with sector not
present in the WC 21 by reading out the missing sector included in
the identical logical cluster address from the NAND memory 10.
[0199] 2. The data managing unit 120 extracts clusters from a track
having only less than 2.sup.(k-i-1) valid clusters tracing tracks
in the WC in order from oldest one and, when the number of valid
clusters reaches 2.sup.k, writes all the clusters in the FSIB 12a
in logical block units.
[0200] 3. When 2.sup.k valid clusters are not found, the data
managing unit 120 writes all track with the number of valid
clusters less than 2.sup.(k-i-1) in the FSIB 12a by the number
equivalent to the number of logical pages.
[0201] 4. The data managing unit 120 invalidates clusters with same
logical cluster address as the clusters copied among those already
present on the FS 12 and the IS 13 after the Copy is finished.
[0202] Update processing for the respective management tables
involved in such Copy processing from the WC 21 to the FSIB 12a is
explained. The data managing unit 120 sets the state flag 25a in
entries corresponding to all clusters in the WC 21 belonging to a
flushed track in the WC cluster management table 25 Invalid.
Thereafter, writing in these entries is possible. Concerning a list
corresponding to the flushed track in the WC track management table
24, the data managing unit 120 changes or deletes, for example, the
next pointer 24d of an immediately preceding list and invalidates
the list.
[0203] On the other hand, when cluster flush from the WC 21 to the
FSIB 12a is performed, the data managing unit 120 updates the
cluster table pointer 30e, the number of FS clusters 31f, and the
like of the track management table 30 according to the cluster
flush. The data managing unit 120 also updates the logical block ID
40b, the intra-logical block cluster position 40c, and the like of
the FS/IS management table 40. Concerning clusters not present in
the FS 12 originally, the data managing unit 120 adds a list to the
linked list of the FS/IS management table 40. According to the
update, the data managing unit 120 updates relevant sections of the
MS logical block management table 35, the FS/IS logical block
management table 42, and the intra-FS/IS cluster management table
44.
CIB Processing
[0204] When the WCF processing explained above is finished, the
logical-NAND-layer managing unit 120b executes CIB processing
including processing for moving the data in the FSIB 12a written by
the WCF processing to the FS 12 and processing for moving the data
in the MSIB 11a written by the WCF processing to the MS 11. When
the CIB processing is started, as explained above, it is likely
that data movement among the blocks and compaction processing are
performed in a chain reacting manner. Time required for the overall
processing substantially changes according to a state. In the CIB
processing, basically, first, the CIB processing in the MS 11 is
performed (step S330), subsequently, the CIB processing in the FS
12 is performed (step S340), the CIB processing in the MS 11 is
performed again (step S350), the CIB processing in the IS 13 is
performed (step S360), and, finally, the CIB processing in the MS
11 is performed again (step S370). In flush processing from the FS
12 to the MSIB 11a, flush processing from the FS 12 to the IS 13,
or flush processing from the IS 13 to the MSIB 11a, when a loop
occurs in a procedure, the processing may not be performed in
order. The CIB processing in the MS 11, the CIB processing in the
FS 12, and the CIB processing in the IS 13 are separately
explained.
CIB Processing in the MS 11
[0205] First, the CIB processing in the MS 11 is explained (step
S330). When movement of track from the WC 21, the FS 12, and the IS
13 to the MS 11 is performed, the track is written in the MSIB 11a.
After the completion of writing in the MSIB 11a, as explained
above, the track management table 30 is updated and the logical
block ID 30c, the intra-block track position 30d, and the like in
which tracks are arranged are changed (Move). When new track is
written in the MSIB 11a, track present in the MS 11 or the TFS 11b
from the beginning is invalidated. This invalidation processing is
realized by invalidating a track from an entry of a logical block
in which old track information is stored in the MS logical block
management table 35. Specifically, a pointer of a relevant track in
a field of the track management pointer 35b in the entry of the MS
logical block management table 35 is deleted and the number of
valid tracks is decremented by one. When all tracks in one logical
block are invalidated by this track invalidation, the valid flag
35e is invalidated. Logical blocks of the MS 11 including invalid
tracks are generated by such invalidation or the like. When this is
repeated, efficiency of use of logical blocks may fall to cause
insufficiency in usable logical blocks.
[0206] When such a situation occurs and the number of logical
blocks allocated to the MS 11 exceeds the upper limit of the number
of logical blocks allowed for the MS 11, the data managing unit 120
performs compaction processing to create a free block FB. The free
block FB is returned to the physical-NAND-layer managing unit 120c.
The logical-NAND-layer managing unit 120b reduces the number of
logical blocks allocated to the MS 11 and, then, acquires a
writable free block FB from the physical-NAND-layer managing unit
120c anew. The compaction processing is processing for collecting
valid clusters of a logical block as a compaction object in a new
logical block or copying valid tracks in the logical block as the
compaction object to other logical blocks to create a free block FB
returned to the physical-NAND-layer managing unit 120c and improve
efficiency of use of logical blocks. In performing compaction, when
valid clusters on the WC 21, the FS 12, and the IS 13 are present,
the data managing unit 120 executes passive merge for merging all
the valid clusters included in a logical track address as a
compaction object. Logical blocks registered in the TFS 11b are not
included in the compaction object.
[0207] An example of Move from the MSIB 11a to the MS 11 or to the
TFS 11b and compaction processing with presence of a full logical
block in the MSIB 11a set as a condition is specifically explained.
The "full" logical block means the logical block in which all
logical pages has been written and additional recording is
impossible.
[0208] 1. Referring to the valid flag 35e of the MS logical block
management table 35, when an invalidated logical block is present
in the MS 11, the data managing unit 120 sets the logical block as
a free block FB.
[0209] 2. The data managing unit 120 moves a full logical block in
the MSIB 11a to the MS 11. Specifically, the data managing unit 120
updates the MS structure management table (not shown) explained
above and transfers the logical block from management under the
MSIB 11a to management under the MS 11.
[0210] 3. The data managing unit 120 judges whether the number of
logical blocks allocated to the MS 11 exceeds the upper limit of
the number of logical blocks allowed for the MS 11. When the number
of logical blocks exceeds the upper limit, the data managing unit
120 executes MS compaction explained below.
[0211] 4. Referring to a field and the like of the number of valid
tracks 35c of the MS logical block management table 35, the data
managing unit 120 sorts logical blocks having invalidated tracks
among logical blocks not included in the TFS 11b with the number of
valid tracks.
[0212] 5. The data managing unit 120 collects tracks from logical
blocks with small numbers of valid tracks and carries out
compaction. In carrying out compaction, first, the tracks are
copied for each of the logical blocks (2.sup.i tracks are copied at
a time) to carry out compaction. When a track as a compaction
object has valid clusters in the WC 21, the FS 12, and the IS 13,
the data managing unit 120 also merges the valid clusters.
[0213] 6. The data managing unit 120 sets the logical block at a
compaction source as a free block FB.
[0214] 7. When the compaction is performed and one logical block
includes the valid 2.sup.i tracks, the data managing unit 120 moves
the logical block to the top of the TFS 11b.
[0215] 8. When the free block FB can be created by copying the
valid tracks in the logical block to another logical block, the
data managing unit 120 additionally records the valid tracks in the
number smaller than 2.sup.i in the MSIB 11a in track units.
[0216] 9. The data managing unit 120 sets the logical block at the
compaction source as the free block FB.
[0217] 10. When the number of logical blocks allocated to the MS 11
falls below the upper limit of the number of logical blocks allowed
for the MS 11, the data managing unit 120 finishes the MS
compaction processing.
CIB Processing in the FS 12
[0218] The CIB processing in the FS 12 is explained (step S340).
When full logical blocks in which all logical pages are written are
created in the FSIB 12a by cluster writing processing from the WC
21 to the FSIB 12a, the logical blocks in the FSIB 12a are moved
from the FSIB 12a to the FS 12. According to the movement, an old
logical block is flushed from the FS 12 of the FIFO structure
configured by a plurality of logical blocks.
[0219] Flush from the FSIB 12a to the FS 12 and flush from the FS
12 to the MS 11 and/or the IS 13 are specifically realized as
explained below.
[0220] 1. Referring to the valid flag 35e and the like of the FS/IS
logical block management table 42, when an invalidated logical
block is present in the FS 12, the data managing unit 120 sets the
logical block as a free block FB.
[0221] 2. The data managing unit 120 flushes a full logical block
in the FSIB 12a to the FS 12. Specifically, the data managing unit
120 updates the FS/IS structure management table (not shown) and
transfers the logical block from management under the FSIB 12a to
management under the FS 12.
[0222] 3. The data managing unit 120 judges whether the number of
logical blocks allocated to the FS 12 exceeds the upper limit of
the number of logical blocks allowed for the FS 12. When the number
of logical blocks exceeds the upper limit, the data managing unit
120 executes flush explained below.
[0223] 4. The data managing unit 120 determines cluster that should
be directly copied to the MS 11 without being moving to the IS 13
among clusters in an oldest logical block as an flush object
(actually, because a management unit of the MS 11 is a track, the
cluster is determined in track units).
[0224] (A) The data managing unit 120 scans valid clusters in the
oldest logical block as the flush object in order from the top of a
logical page.
[0225] (B) The data managing unit 120 finds, referring to a field
of the number of FS clusters 30f of the track management table 30,
how many valid clusters a track to which the cluster belongs has in
the FS 12. [0226] (C) When the number of valid clusters in the
track is equal to or larger than a predetermined threshold (e.g.,
50% of 2.sup.k-1), the data managing unit 120 sets the track as a
candidate of flush to the MS 11.
[0227] 5. The data managing unit 120 writes the track that should
be flushed to the MS 11 in the MSIB 11a.
[0228] 6. When valid clusters to be flushed in the track units are
left in the oldest logical block, the data managing unit 120
further executes flush to the MSIB 11a.
[0229] 7. When valid clusters are present in the logical block as
the flush object even after the processing of 2 to 4 above, the
data managing unit 120 moves the oldest logical block to the IS
13.
[0230] When flush from the FS 12 to the MSIB 11a is performed,
immediately after the flush, the data managing unit 120 executes
the CIB processing in the MS 11 (step s350).
CIB Processing in the IS 13
[0231] The CIB processing in the IS 13 is explained (step S360).
The logical block is added to the IS 13 according to the movement
from the FS 12 to the IS 13. However, according to the addition of
the logical block, the number of logical blocks exceeds an upper
limit of the number of logical blocks that can be managed in the IS
13 formed of a plurality of logical blocks. When the number of
logical blocks exceeds the upper limit, in the IS 13, the data
managing unit 120 performs flush of one to a plurality of logical
blocks to the MS 11 and executes IS compaction. Specifically, the
data managing unit 120 executes a procedure explained below.
[0232] 1. The data managing unit 120 sorts tracks included in the
IS 13 with the number of valid clusters in the track.times.a valid
cluster coefficient, collects 2.sup.i+1 tracks (for two logical
blocks) with a large value of a product, and flushes the tracks to
the MSIB 11a.
[0233] 2. When a total number of valid clusters of 2.sup.i+1
logical blocks with a smallest number of valid clusters is, for
example, equal to or larger than 2.sup.k (for one logical block),
which is a predetermined set value, the data managing unit 120
repeats the step explained above.
[0234] 3. After performing the flush, the data managing unit 120
collects 2.sup.k clusters in order from a logical block with a
smallest number of valid clusters and performs compaction in the IS
13.
[0235] 4. The data managing unit 120 releases a logical block not
including a valid cluster among the logical blocks at compaction
sources as a free block FB.
[0236] When flush from the IS 13 to the MSIB 11a is performed,
immediately after the flush, the data managing unit 120 executes
the CIB processing in the MS 11 (step S370).
[0237] FIG. 20 is a diagram of combinations of inputs and outputs
in a flow of data among components and indicates what causes the
flow of the data as a trigger. Basically, data is written in the FS
12 according to cluster flush from the WC 21. However, when
intra-cluster sector padding (cluster padding) is necessary
incidentally to flush from the WC 21 to the FS 12, data from the FS
12, the IS 13, and the MS 11 is copied. In the WC 21, it is
possible to perform management in sector (512 B) units by
identifying presence or absence of 2.sup.(l-k) sectors in a
relevant logical cluster address using the sector position bitmap
25b in the tag of the WC cluster management table 25. On the other
hand, a management unit of the FS 12 and the IS 13, which are
functional components in the NAND memory 10, is a cluster and a
management unit of the MS 11 is a track. In this way, a management
unit in the NAND memory 10 is larger than the sector. Therefore, in
writing data in the NAND memory 10 from the WC 21, when data with a
logical cluster address identical with that of the data to be
written is present in the NAND memory 10, it is necessary to write
the data in the NAND memory 10 after merging a sector in a cluster
to be written in the NAND memory 10 from the WC 21 and a sector in
the identical logical cluster address present in the NAND memory
10.
[0238] This processing is the intra-cluster sector padding
processing (the cluster padding) and the intra-track sector padding
(the track padding) shown in FIG. 20. Unless these kinds of
processing are performed, correct data cannot be read out.
Therefore, when data is flushed from the WC 21 to the FSIB 12a or
the MSIB 11a, the WC cluster management table 25 is referred to and
the sector position bitmaps 25b in tags corresponding to clusters
to be flushed is referred to. When all the sector position bitmaps
25b are not "1", the intra-cluster sector padding or the
intra-track sector padding for merging with a sector in an
identical cluster or an identical track included in the NAND memory
10 is performed. A work area of the DRAM 20 is used for this
processing. A plurality of sectors included in a logical cluster
address or a logical track address is merged on the work area of
the DRAM 20 and data image (cluster image or track image) to be
flushed is created. The created data image is written in the MSIB
11a or written in the FSIB 12a from the work area of the DRAM
20.
[0239] In the IS 13, basically, data is written according to block
flush from the FS 12 (Move) or written according to compaction in
the IS. In the MS 11, data can be written from all sections. When
the data is written, in the MS 11, padding due to data of the MS
itself can be caused because data can only be written in track
units. When the data is written in track units, fragmented data in
other logical blocks are also written according to passive merge.
Moreover, in the MS 11, data is also written according to MS
compaction. In the passive merge, when track flush or logical block
flush (flush for 2.sup.i tracks) from one of three components of
the WC 21, the FS 12, or the IS 13 to the MS 11 is performed, valid
clusters in two components included in a track (or a logical block)
as an flush object in one component and valid clusters in the MS 11
are collected in the work area of the DRAM 20 and written in the
MSIB 11a from the work area of the DRAM 20 as data for one
track.
[0240] This embodiment is explained more in detail. FIG. 21 is a
diagram of a detailed functional configuration related to the write
processing of the NAND memory 10 shown in FIG. 6. Redundant
explanation is omitted.
FS Configuration
[0241] An FS unit 12Q includes the FSIB 12a and the FS 12. The FS
12 has a capacity for a large number of logical blocks. The FIFO
structure is managed in logical block units. The FS input buffer
(FSIB) 12a to which data flushed from the WC 21 is input is
provided at a pre-stage of the FS 12. The FSIB 12a includes an FS
full block buffer (FSFB) 12aa and an FS additional recording buffer
(FS additional recording IB) 12ab. The FSFB 12aa has a capacity for
one to a plurality of logical blocks. The FS additional recording
IB 121ab also has a capacity for one to a plurality of logical
blocks. When the data flushed from the WC 21 is data for one
logical block, data copy in logical block units (block Copy) to the
FSFB 12aa is performed. When the data is not the data for one
logical block, data copy in logical page unit (page Copy) to the FS
additional recording IB 12ab is performed.
IS Configuration
[0242] An IS unit 13Q includes the IS 13, an IS input buffer (ISIB)
13a, and an IS compaction buffer 13c. The ISIB 13a has a capacity
for one to a plurality of logical blocks, the IS compaction buffer
13c has a capacity for, for example, one logical block, and the IS
13 has a capacity for a large number of logical blocks. In the IS
13, as in the FS 12, the FIFO structure is managed in logical block
units. The IS compaction buffer 13c is a buffer for performing
compaction in the IS unit 13Q.
[0243] As explained above, the IS unit 13Q performs management of
data in cluster units in the same manner as the FS unit 12Q. When
movement of a logical block from the FS unit 12Q to the IS unit
13Q, i.e., flush from the FS 12 is performed, a logical block as an
flush object, which is a previous management object of the FS unit
12Q, is changed to a management object of the IS unit 13
(specifically, the ISIB 13a) according to relocation of a pointer
(block Move). When the number of logical blocks of the IS 13
exceeds a predetermined upper limit according to the movement of
the logical block from the FS unit 12Q to the IS unit 13Q, data
flush from the IS 13 to an MS unit 11Q and IS compaction processing
are executed and the number of logical blocks of the IS unit 13Q is
returned to a specified value.
MS Configuration
[0244] The MS unit 11Q includes the MSIB 11a, the track pre-stage
buffer (TFS) 11b, and the MS 11. The MSIB 11a includes one to a
plurality of (in this embodiment, four) MS full block input buffers
(hereinafter, MSFBs) 11aa and one to a plurality of (in this
embodiment, two) additional recording input buffers (hereinafter,
MS additional recording IBs) 11ab. One MSFB 11aa has a capacity for
one logical block. The MSFB 11aa is used for writing in logical
block units. One MS additional recording IB 11ab has a capacity for
one logical block. The MS additional recording IB 11ab is used for
additional writing in track units.
[0245] A logical block flushed from the WC 21, a logical block
flushed from the FS 12, or a logical block flushed from the IS 13
is copied to the MSFB 11aa (block Copy). The logical block copied
to one MSFB 11aa is directly moved to the MS 11 (block Copy)
without being moved through the TFS 11b. After the logical block is
moved to the MS 11, a free block FB is allocated as the MSFB
11aa.
[0246] A track flushed from the WC 21 or a track flushed from the
FS 12 is copied to the MS additional recording IB 11ab in appending
manner (track Copy). A full logical block in such MS additional
recording IB 11ab additionally recorded in track units is moved to
the TFS 11b (block Move). After the logical block is moved to the
TFS 11b, a free block FB is allocated as the MS additional
recording IB 11ab.
[0247] As explained above, the TFS 11b is a buffer that has a
capacity for a large number of logical blocks and has the FIFO
structure interposed between the MS additional recording IB 11ab
and the MS 11. A full logical block in the MS additional recording
IB 11ab additionally recorded in track units is moved to an input
side of the TFS 11b having the FIFO structure. A logical block
having valid data, formed according to the compaction processing in
the MS 11, is moved from the MS compaction buffer 11c (block Move).
The MS compaction buffer 11c is a buffer for performing compaction
in the MS 11. When a track in the MS is written in the MS
compaction buffer 11c according to the compaction processing in the
MS 11, passive merge for writing valid clusters in the WC 21, the
FS unit 12Q, and the IS unit 13Q, which are included in the track
as a writing object, in the MS compaction buffer 11c via the work
area of the DRAM 20 is performed. In this embodiment, logical
blocks registered in the MSIB 11a and the TFS 11b are not included
in the compaction object.
[0248] FIG. 22 is a diagram of a more detailed functional
configuration of the data managing unit 120. As explained above,
the data managing unit 120 includes the DRAM-layer managing unit
120a that performs management of data stored in the DRAM 20, the
logical-NAND-layer managing unit 120b that performs management of
data stored in the NAND memory 10, and the physical-NAND-layer
managing unit 120c that manages the NAND memory 10 as a physical
storage device.
[0249] The DRAM-layer managing unit 120a includes the RC cluster
management table 23, the WC cluster management table 25, and the WC
track management table 24 and performs management of a DRAM layer
based on the management tables. The logical-NAND-layer managing
unit 120b includes, besides the track management table 30, the MS
block management table 35, the FS/IS management table 40, the FS/IS
logical block management table 42, and the intra-FS/IS cluster
management table 44, an MS structure management table 60 and an
FS/IS structure management table 65 and performs management of a
logical NAND layer of the NAND memory 10 based on the management
tables. The physical-NAND-layer managing unit 120c includes,
besides the logical-to-physical translation table 50, a bad block
management table (BB management table) 200, a reserved block
management table (RB block management table) 210, a free block
management table (FB management table) 220, and an active block
management table (AB management table) 230 and performs management
of a physical NAND layer of the NAND memory 10 using the management
tables.
Physical NAND Layer
[0250] First, the physical NAND layer is explained. As explained
above, in the 32-bit double speed mode, four channels (ch0, ch1,
ch2, and ch3) are actuated in parallel and erasing, writing, and
readout are performed by using a double speed mode of an NAND
memory chip. As shown in FIG. 23, each of NAND memory chips in the
four parallel operation elements 10a to 10d is divided into, for
example, two districts of a plane 0 and a plane 1. The number of
division is not limited to two. The plane 0 and the plane 1 include
peripheral circuits independent from one another (e.g., a row
decoder, a column decoder, a page buffer, and a data cache) and can
simultaneously perform erasing, writing, and readout based on a
command input from the NAND controller 112. In the double speed
mode of the NAND memory chip, high-speed writing is realized by
controlling the plane 0 and the plane 1 in parallel.
[0251] A physical block size is 512 kB. Therefore, in the 32-bit
double speed mode, an erasing unit of the physical block is
increased to 512 kB.times.4.times.2=4 MB according to the parallel
operation of the four channels and the simultaneous access to the
two planes. As a result, in the 32-bit double speed mode, eight
planes operate in parallel.
[0252] FIG. 24 is a diagram of another example of the
logical-to-physical translation table 50. In the
logical-to-physical translation table 50 shown in FIG. 24, a field
of erasing time 50e indicating time when a logical block
corresponding to the logical block ID 50a is erased is added to the
logical-to-physical table 50 shown in FIG. 17. As the erasing time
50e, for example, a value obtained by measuring the number of times
an erasing operation is applied to the logical blocks in the NAND
memory chip or energization time of the NAND controller 112 only
has to be used. The erasing time 50e is used for free block FB
management in the FB management table 220 explained later.
[0253] The BB management table 200 is a table for managing bad
blocks BB in physical block (512 kB) units. As shown in FIG. 25,
the BB management table 200 is formed in a two-dimensional array
format having, for example, for every 4 (channels).times.2
(planes/channels) intra-channel planes, information concerning
physical blocks for (the number of physical
blocks/planes).times.(the number of NAND memory chips/one parallel
operation element). In each entry of the BB management table 200, a
physical block ID 200a for each physical block is stored.
[0254] In the case of this embodiment, one NAND memory chip has a 2
GB size. Physical block IDs "0" to "2047" are allocated to a plane
0 of a first chip. Physical block IDs "2048" to "4095" are
allocated to a plane 1 of the first chip. When the bad block BB
generated during use is registered in the BB management table 200,
the physical-NAND-layer managing unit 120c adds bad blocks BB
immediately behind last valid entries of intra-channel plane IDs
(ID#0 to ID#7) corresponding thereto without sorting the bad blocks
BB.
[0255] For example, a physical block for which, when a use is
allocated to a free block FB, an erasing operation is not normally
finished is registered as the bad block BB, or for which, when data
is written in a active block AB used as the FS 12, IS 13, or MS 11,
writing operation is not normally finished may be registered as the
bad block BB.
[0256] The RB management table 210 is a table for managing physical
blocks (reserved blocks RB) remaining when 4 MB logical blocks are
formed in eight physical block units (512 kB). The RB management
table 210 is managed in a format same as that of the BB management
table 200. By managing the blocks in FIFO for each of intra-channel
plane IDs corresponding thereto, the reserved blocks RB are
preferentially used in order from one registered earliest.
[0257] The FB management table 220 is a table for managing free
blocks FB presently not allocated to a use (e.g., use for the FS12,
IS 13, or MS11) in 4 MB logical block units and is a list in the
FIFO format sorted in order of creation of the free blocks FB. A
logical block ID is stored in each entry. The free block FB
returned to the FB management table 220 according to compaction
processing or the like is added to the tail end of the list. Free
block FB allocation is performed by returning a top block of the
list.
[0258] As shown in FIG. 26, the FB management table is configured
in two stages of a return FIFO list 220a and an allocation list
220b. The return FIFO list 220a is aligned in order of the erasing
time 50e. In the allocation list 220b, a logical block with a
smaller number of times of erasing 50c is located closer to the top
of the list. This is a configuration for preventing an erasing
operation from being repeated at short time intervals. An
unnecessary logical block returned to the FB management table 220
is added to the tail end of the return FIFO list 220a and stored
there for a fixed period.
[0259] A logical block pushed out from the return FIFO list 220a is
inserted in somewhere in the allocation list 220b according to the
number of times of erasing 50c of the logical block. When
allocation of the free block FB is requested from the
logical-NAND-layer managing unit 120b, the logical-NAND-layer
managing unit 120c extracts the free block FB from the top of the
allocation list 220b and allocates the free block FB.
[0260] With the FB management table, it is possible to equally
distribute logical blocks to be erased (wear leveling processing)
such that the numbers of times of erasing and erasing intervals of
all logical blocks are generally equal. It is known that the life
of a NAND-type flash memory depends on intervals of erasing
processing besides the number of times of erasing and, as the
intervals are longer, retention properties are better and the life
is longer. This also indicates that, when the erasing intervals are
short, the retention properties are bad and the life is spoiled. It
is also known that, even if writing is performed at short
intervals, unless appropriate long term erasing is performed, the
retention properties are recovered.
[0261] The AB management table 230 is a list of logical blocks
(active blocks AB), to which a use (e.g., use for the FS12, IS 13,
or MS11) are allocated, allocated from the free blocks FB. As in
the FB management table 220, in the AB management table 230, a
logical block ID is stored in each entry. A logical block with
earlier registration order is located closer to the top. The AB
management table is used for, for example, refresh processing.
[0262] The refresh processing is a technique for preventing an
error exceeding error correction ability of the SSD 110 from
occurring because of the influence of aged deterioration of written
data and read disturb, which is data breakage involved in read
processing. Specifically, for example, before an error exceeding
the error correction ability occurs, processing for reading out
stored data and performing error correction and, then, rewriting
the data in the NAND-type flash memory is performed. For example, a
block with a large number of times of readout 50d, a top block of
the AB management table 230, and the like can be set as monitoring
objects of the refresh processing.
[0263] The physical-NAND-layer managing unit 120c performs logical
block/physical block management explained below. First, a
correspondence relation between a logical block ID and eight
physical block IDs in the logical-to-physical translation table 50
is explained with reference to FIG. 27.
[0264] As explained above, eight physical block IDs associated with
the logical block ID 50a as an index of the logical-to-physical
translation table 50 are registered in fields of the physical block
ID 50b of the logical-to-physical translation table 50. FIG. 27 is
a diagram of a correspondence relation between logical block IDs
and physical block IDs of the NAND memory 10. One section
represents one physical block. A physical block ID is allocated to
each of the physical blocks. A logical block L0 (active block AB)
includes, for example, eight physical blocks in the first row and
the third column, the second row and the second column, the third
row and the second column, the fourth row and the second column,
the fifth row and the second column, the six row and the second
column, the seventh row and the second column, and the eighth row
and the third column. A logical block L1 (active block AB)
surrounded by a broken line BL1 includes, for example, eight
physical blocks in the first row and a fourth column, the second
row and the third column, the third row and the third column, the
fourth row and the third column, the fifth row and the third
column, the sixth row and the third column, the seventh row and the
third column, and the eighth row and the fourth column.
[0265] Thereafter, for example, it is assumed that, when a use is
allocated to the logical block L1 (in this case, the logical block
L1 is the free block FB) and erasing operation is executed or when
data is written in the logical block L1 used as the FS 12, IS 13,
or MS 11 (in this case, the logical block L1 is the active block AB
as shown in FIG. 27) and writing operation is executed, the erasing
or writing operation for the physical block in the fourth row and
the third column of the logical block L1 is not normally finished,
and as a result, the physical block is registered in the BB
management table 200 as the bad block BB that cannot be used as a
storage area.
[0266] The physical-NAND-layer managing unit 120c detects the
registration and selects, as a replacement candidate for the bad
block BB, the reservation block RB in a channel and a plane
identical with those of the physical block registered as the bad
block BB from the RB management table 210.
[0267] In the case of FIG. 27, a physical block (the reserved block
RB) in the fourth row and the fourth column adjacent to the bad
block BB is selected as a replacement candidate for the bad block
BB in the fourth row and the third column.
[0268] The physical-NAND-layer managing unit 120c searches through
an entry of the logical block ID 50a corresponding to the logical
block L1 of the logical-to-physical translation table 50 and
changes a physical block ID of the bad block BB corresponding to
the fourth row and the third column among the eight physical block
IDs included in a field of the physical block ID 50b in the entry
to a physical address ID corresponding to the reserved block RB in
the fourth row and the fourth column selected from the RB
management table 210.
[0269] Consequently, thereafter, the logical block L1 includes a
combination of eight new physical blocks in the first row and the
fourth column, the second row and the third column, the third row
and the third column, the fourth row and the fourth column, the
fifth row and the third column, the sixth row and the third column,
the seventh row and the third column, and the eighth row and the
fourth row surrounded by an alternate long and short dash line. It
is assumed that a logical block ID of the logical block L1 is
"L1".
[0270] Thereafter, the physical-NAND-layer managing unit 120c
secures a new free block FB (not shown in FIG. 27) from the FB
management table 220. It is assumed that a logical block ID of the
secured free block FB is "L2". The physical-NAND-layer managing
unit 120c executes replacement of the logical block IDs using the
logical-to-physical translation table 50.
[0271] Specifically, the physical-NAND-layer managing unit 120c
associates the eight physical blocks, which are associated with the
new free block FB with the logical block ID "L2", with the logical
block ID "L1". At the same time, the physical-NAND-layer managing
unit 120c associates the eight physical blocks in the first row and
the fourth column, the second row and the third column, the third
row and the third column, the fourth row and the fourth column, the
fifth row and the third column, the sixth row and the third column,
the seventh row and the third column, and the eighth row and the
fourth column surrounded by the alternate long and short dash line
with the logical block ID "L2". The number of times of erasing 50c,
the number of times of readout 50d, and the erasing time 50e are
also replaced according to the update of the physical block IDs.
Thereafter, the physical-NAND-layer managing unit 120c registers
the logical block ID "L2" in the FB management table 220. The
logical-NAND-layer managing unit 120b executes erasing or writing
operation in the newly secured logical block with the same logical
block ID "L1" afresh.
[0272] On the other hand, when the reserved block RB that can be
replaced with the bad block BB is not present, the
physical-NAND-layer managing unit 120c performs processing
explained below. For example, it is assumed that the physical block
in the fourth row and the third column is registered in the BB
management table 200 as the bad block BB and the reserved block RB
is not present in an identical channel and an identical plane for
the bad block BB. In this case, first, the physical-NAND-layer
managing unit 120c registers the seven physical blocks in the first
row and the fourth column, the second row and the third column, the
third row and the third column, the fifth row and the third column,
the sixth row and the third column, the seventh row and the third
column, and the eighth row and the fourth column excluding the
fourth row and the third column in the logical block L1 in the RB
management table 210. Thereafter, in the same manner as explained
above, the physical-NAND-layer managing unit 120c secures a new
free block FB from the FB management table 220 and executes
replacement of the logical block IDs as explained above, and, then,
sets the logical block ID acquired from the FB management table 220
unusable.
[0273] In this way, even when the bad block BB is generated, the
physical-NAND-layer managing unit 120c is executing replacement of
the logical block IDs. Therefore, the logical block ID used in the
logical-NAND-layer managing unit 120b does not change before and
after the generation of the bad block BB. Therefore, even when at
least one of a plurality of physical blocks is registered as a bad
block, a correspondence relation between LBA logical addresses and
logical blocks is not changed. It is possible to prevent overhead
of rewriting of the management tables in the logical-NAND-layer
managing unit 120b.
[0274] In the 8-bit normal mode for independently driving one plane
in the parallel operation elements 10a to 10d, an erasing unit of
the mode is one physical block (512 KB). The 8-bit normal mode is
used when a writing size is small, for example, when a log for
recording updated contents of the management tables is additionally
written.
[0275] When the free block FB used in such an 8-bit normal mode,
i.e., a physical block in 512 KB units is necessary, the
physical-NAND-layer managing unit 120c secures 4 MB logical block
in the 32-bit double speed mode and selects one physical block in
the secured logical block. FIG. 27 indicates that a logical block
L3 surrounded by a broken line BL3 including one physical block
surrounded by a thick line, which is used soon in the
logical-NAND-layer managing unit 120b, is assigned.
[0276] In the 8-bit normal mode, first, the physical-NAND-layer
managing unit 120c uses the selected one physical block. When the
one physical block is filled with data because of the additional
recording of the log, the physical-NAND-layer managing unit 120c
uses another physical block among the eight physical blocks in the
logical block L3. Thereafter, such processing is repeated.
[0277] Erasing processing in the 32-bit double speed mode is
explained. The physical-NAND-layer managing unit 120c counts up,
every time data in the NAND memory 10 is erased in logical block
units, a field of the number of times of erasing 50c in a logical
block ID corresponding to an erased logical block of the
logical-to-physical translation table 50 shown in FIG. 24 by one
and updates the erasing time 50e to latest data.
Logical NAND Layer
[0278] The MS structure management table 60 and the FS/IS structure
management table 65 used for management in a logical NAND layer are
explained with reference to FIGS. 28 and 29. The MS structure
management table 60 shown in FIG. 28 includes an area for managing
the structure of the MS unit 11Q and an area for storing state
information. The MS structure management table 60 includes an MS
buffer management table 61 for managing logical block IDs allocated
as the MSFB 11aa, the MS additional recording IB 11ab, and the TFS
11b, a logical block ID list by the number of valid tracks 62 for
storing logical block IDs with a small number of valid tracks in
order to increase the speed of sort processing during the MS
compaction, and areas 63 and 64 for managing a maximum number of
logical blocks MBL and the number of valid logical blocks VBL as
state information.
[0279] In the MS structure management table 60, fixed fields 61a to
61c with a required number of entries are prepared for the MSFB
11aa, the MS additional recording IB 11ab, and the TFS 11b. Logical
block IDs are recorded in the fixed fields 61a to 61c. The field
61c for the TFS 11b has the linked list structure. FIFO-like
management for the TFS 11b having the FIFO structure is
performed.
[0280] In the logical block ID list by the number of valid tracks
62, a required number of entries are prepared for a logical block
with one valid track, a required number of entries are prepared for
a logical block with two valid tracks, . . . , and a required
number of entries are prepared for a logical block with 2.sup.i-1
valid tracks. A logical block ID is recorded in each of the
entries. When a field of the number of valid tracks 35c of the MS
logical block management table 35 is searched, the logical block ID
list by the number of valid tracks 62 is always updated to a latest
state. Logical blocks registered in the MS buffer management table
61 as the MSIB 11a and the TFS 11b are not entered in the logical
block ID list by the number of valid tracks 62.
[0281] In the fixed field 63 for the maximum number of logical
blocks MBL as state information, a maximum number of logical blocks
MBL as the number of logical blocks that the MS unit 11Q is allowed
to acquire is recorded. In the fixed field 64 for the number of
valid logical blocks VBL as state information, the number of valid
logical blocks VBL as the number of logical blocks presently
managed as the MS unit 11Q is recorded.
[0282] The FS/IS structure management table 65 shown in FIG. 29 has
an area for managing the structure of the FS unit 12Q and the IS
unit 13Q. The FS/IS structure management table 65 includes an FS
input buffer management table 66 for managing logical block ID
allocated as the FSIB 12a and the FS additional recording IB 12ab,
an FS FIFO management table 67 for managing the FIFO structure of
the FS 12, an IS input buffer management table 68 for managing a
logical block ID allocated as the ISIB 13a, and the IS FIFO
management table 69 for managing the FIFO structure of the IS
13.
[0283] In the FS input buffer management table 66, fixed fields 66a
and 66b with a required number of entries are prepared for the FSFB
12aa and the FS additional recording IB 12ab. The FS/IS block ID
42a as an index of the FS/IS logical block management table 42 is
registered in the fixed fields 66a and 66b. In the IS input buffer
management table 68, fixed fields with a required number of entries
are prepared for the ISIB 13a. The FS/IS block ID 42a is registered
in the fixed fields. In the FS FIFO management table 67, entries
for the number of logical blocks forming the FIFO structure of the
FS 12 are prepared in fixed fields. The FS/IS block ID 42a is
registered in the fixed fields of the FS FIFO management table 67.
In the IS FIFO management table 69, entries for the number of
logical blocks forming the FIFO structure of the IS 13 are prepared
in fixed fields. The FS/IS block ID 42a is registered in the fixed
fields.
[0284] Update processing for the management tables involved in the
Copy processing from the WC 21 to the MSIB 11a in executing the
write processing divided into the two stages (the WCF processing
and the CIB processing) explained with reference to FIG. 19 is
explained. Here, Copy in track units from the WC 21 to the MS
additional recording IB 11ab is performed. The DRAM-layer managing
unit 120a checks the WC track management table 24 in order from the
top, referring to the way-line bitmap 24c in a track entry in which
the logical track address 24a corresponding to a track decided to
be flushed is registered, changes the state flag 25a in an entry in
the WC cluster management table 25 corresponding to an entry with a
valid bit "1" in m.times.n entries of the way-line bitmap 24c from
Valid to a wait for flush to a NAND, and notifies the
logical-NAND-layer managing unit 120b of an flush request.
[0285] On the other hand, the logical-NAND-layer managing unit 120b
checks a state of the MS additional recording IB 11ab referring to
the MS buffer management table 61 of the MS structure management
table 60 shown in FIG. 28 and the MS logical block management table
35 shown in FIG. 14. When it is judged from the field 61b for the
MS additional recording IB of the MS buffer management table 61
that the MS additional recording IB 11ab is already present, the
logical-NAND-layer managing unit 120b acquires information
concerning the number of writable tracks for a logical block ID
registered in the field 61b for the MS additional recording IB from
the field of the number of valid tracks 35c of the MS logical block
management table 35 and notifies the DRAM-layer managing unit 120a
of the acquired number of writable tracks.
[0286] When it is judged from the field 61b for the MS additional
recording IB of the MS buffer management table 61 that the MS
additional recording IB 11ab is not present, the logical-NAND-layer
managing unit 120b issues a request for acquiring the free block FB
to the physical-NAND-layer managing unit 120c and acquires the free
block FB together with a logical block ID allocated as the free
block FB. The logical-NAND-layer managing unit 120b notifies the
DRAM-layer managing unit 120a of the number of writable tracks 21
of the acquired free block FB.
[0287] The DRAM-layer managing unit 120a selects tracks from the WC
track management table 24 by the number of writable tracks notified
from the logical-NAND-layer managing unit 120b and judges whether
the intra-track sector padding is performed. In order to check
whether clusters and/or tracks included in range of the logical
track addresses to be flushed is present in the NAND memory 10 and
judges whether the intra-track sector padding is performed, the
DRAM-layer managing unit 120a notifies the logical-NAND-layer
managing unit 120b of required information such as a logical track
address to be flushed.
[0288] When the logical-NAND-layer managing unit 120b receives this
notification, the logical-NAND-layer managing unit 120b searches
through the logical track address 30a as an index of the track
management table 30 and, when necessary, further searches through
the FS/IS management table 40, and judges whether a logical track
address identical with the logical track address to be flushed is
present on the NAND memory 10. The logical-NAND-layer managing unit
120b notifies the physical-NAND-layer managing unit 120c of a
result of the search. Consequently, the physical-NAND-layer
managing unit 120c performs flush from the WC 21 to the MS
additional recording IB 11ab involving the intra-track sector
padding or not involving the intra-track sector padding.
[0289] When the finish of the flush from the WC 21 to the MS
additional recording IB 11ab is notified from the
physical-NAND-layer managing unit 120c, if a new free block FB is
acquired from the physical-NAND-layer managing unit 120c as the MS
additional recording IB 11ab, the logical-NAND-layer managing unit
120b sets the valid flag 35e of an entry of the MS logical block
management table 35 corresponding to a logical block ID of the free
block FB given from the physical-NAND-layer managing unit 120c
valid, registers the logical block ID in the field 61b for the MS
additional recording IB of the MS buffer management table 61, and
increments the number of valid logical blocks VBL of the MS
structure management table 60.
[0290] The logical-NAND-layer managing unit 120b updates the track
management table 30. In other words, the logical-NAND-layer
managing unit 120b registers required information such as the
cluster bit map 30b, the logical block ID 30c, and the
intra-logical block track position 30d in an entry of the logical
track address 30a corresponding to the track flushed from the WC 21
to the MS additional recording IB 11ab.
[0291] When an old track having the identical logical track address
is not present in the NAND memory 10 and the intra-track sector
padding is not performed, the logical-NAND-layer managing unit 120b
registers required information concerning the new track flushed
from the WC 21 in an entry corresponding to the logical track
address of the track management table 30. The logical-NAND-layer
managing unit 120b registers information concerning the track
flushed from the WC 21 in an entry corresponding to a written
logical block ID of the MS logical block management table 35. As
the registration in the MS logical block management table 35, there
are, for example, update of the logical track address (the track
management pointer 35b) as an index of the track management table
30 corresponding to the tracks stored in the logical block
allocated to the MS 11, update of the number of valid tracks 35c,
and update of the writable top track 35d.
[0292] When an old track having the identical logical track address
is present in the NAND memory 10 (the old track is superseded) and
the intra-track sector padding is performed, the logical-NAND-layer
managing unit 120b updates required information such as the logical
block ID 30c and the intra-logical block track position 30d in an
entry of the logical track address 30a corresponding to a merge
source track in the track management table 30. Specifically, the
logical-NAND-layer managing unit 120b changes the logical block ID
30c from an old logical block ID in the MS 11 to which the merge
source track is associated to a new logical block ID corresponding
to the MS additional recording IB 11ab. The intra-logical block
track position 30d is changed according to an additional recording
state.
[0293] Moreover, the logical-NAND-layer managing unit 120b deletes
a relevant section of a field of the track management pointer 35b
in an entry corresponding to the old logical block ID to which the
merge source track is associated in the MS logical block management
table 35, decrements the number of valid tracks 35c, and updates
the logical block ID list by the number of valid tracks 62 of the
MS structure management table 60. When the number of valid tracks
35c in the entry corresponding to the old logical block ID to which
the merge source track is associated is reduced to 0 by the
decrement, the logical-NAND-layer managing unit 120b decrements the
number of valid logical blocks VBL of the MS structure management
table 60 and returns the logical block as the free block FB to the
physical-NAND-layer managing unit 120c. The logical-NAND-layer
managing unit 120b sets the valid flag 35e of the entry
corresponding to the released logical block invalid. Moreover, in
the same manner as explained above, the logical-NAND-layer managing
unit 120b registers information concerning the new track flushed
from the WC 21 in the MS logical block management table 35.
[0294] When the completion of flush from the WC 21 to the MS
additional recording IB 11ab is notified from the
physical-NAND-layer managing unit 120c, the logical-NAND-layer
managing unit 120b notifies the DRAM-layer managing unit 120a of
the completion of the flush (WCF processing). The DRAM-layer
managing unit 120a receives the notification and sets the state
flags 25a in entries corresponding to all clusters belonging to the
flushed track in the WC cluster management table 25 invalid
(usable). Thereafter, writing of data from the host apparatus 1 in
the entries is possible. Concerning a list corresponding to the
flushed track in the WC track management table 24, for example, the
next pointer 24d of an immediately preceding list is changed or
deleted and the list is invalidated.
[0295] The CIB processing is explained. When the WCF processing is
finished, the CIB processing including processing for moving the
data of the FSIB 12a written by the WCF processing to the FS 12 and
processing for moving the data of the MSIB 11a written by the WCF
processing to the MS 11 or the TFS 11b is executed. A detailed
procedure of the CIB processing is explained below with reference
to a flowchart shown in FIG. 30.
CIB Processing in the MS Unit 11Q
[0296] First, the CIB processing in the first time in the MS unit
11Q explained at step S330 in FIG. 19 is explained in detail. The
logical-NAND-layer managing unit 120b acquires, from a field of the
number of valid tracks 35c of the MS logical block management table
35, information of the number of valid tracks concerning logical
block IDs registered in the field 61a for the MSFB and the field
61b for the MS additional recording IB of the MS buffer management
table 61 of the MS structure management table 60. The
logical-NAND-layer managing unit 120b checks whether one or more
full blocks, in which all logical pages are written with tracks,
are present in the MSFB 11aa or the MS additional recording IB 11ab
of the MSIB 11a (step S400). When one or more full blocks are
present in the MSIB 11a, the logical-NAND-layer managing unit 120b
performs the processing explained below. When the judgment at step
S400 is NO, the procedure shifts to step S440.
[0297] When the judgment at step S400 is YES, the
logical-NAND-layer managing unit 120b checks whether an invalid
logical block, the number of valid tracks 35c of which is 0, is
present in the MS referring to the number of valid tracks 35c of
the MS logical block management table 35. When the invalid logical
block is present in the MS, the logical-NAND-layer managing unit
120b returns the invalid logical bock to the physical-NAND-layer
managing unit 120c (step S405). In an entry of the MS logical block
management table 35 corresponding to the returned invalid logical
block, the valid flag 35e is set invalid and the number of valid
logical blocks VBL of the MS structure management table 60 is
decremented. The logical-NAND-layer managing unit 120b directly
moves a full logical block in the MSFB 11aa to the MS 11 and moves
a full logical block in the MS additional recording IB 11ab to the
TFS 11b (step S407). This Move processing is processing for only
deleting relevant logical block IDs registered in the field 61a for
the MSFB and the field 61b for the MS additional recording IB of
the MS buffer management table 61 of the MS structure management
table 60.
[0298] The logical-NAND-layer managing unit 120b compares the
number of valid logical blocks VBL as state information of the MS
structure management table 60 with the maximum number of logical
blocks MBL (step S410). As a result of the comparison, when the
number of valid logical blocks VBL exceeds the maximum number of
logical blocks MBL, the logical-NAND-layer managing unit 120b
judges that the free blocks FB are insufficient, executes MS
compaction processing explained below block by block, increases
invalid logical blocks that should be returned to the
physical-NAND-layer managing unit 120c entirely configured by
invalid tracks, and reduces the number of valid logical blocks VBL
to be smaller than the maximum number of blocks MBL (step S420).
When the free blocks FB are not insufficient in the judgment at
step S410, the procedure is shifted to step S440.
[0299] As the MS compaction processing, as explained above, there
are two types, i.e., 2.sup.i track MS compaction and less than
2.sup.i track MS compaction. In the 2.sup.i track MS compaction,
the MS compaction buffer 11c is used and a logical block used as
the MS compaction buffer 11c after the compaction is moved to the
top of the TFS 11b. In the less than 2.sup.i track MS compaction,
valid tracks are copied to the MS additional recording IB 11ab.
[0300] First, the logical-NAND-layer managing unit 120b executes
the 2.sup.i track MS compaction for collecting 2.sup.i tracks from
logical blocks with a small number of valid tracks referring to the
logical block ID list by the numbers of valid tracks 62 of the MS
structure management table 60 and copying the collected 2.sup.i
tracks to the MS compaction buffer 11c acquired from the
physical-NAND-layer managing unit 120c.
[0301] Specifically, the logical-NAND-layer managing unit 120b
issues an acquisition request for a free block FB to the
physical-NAND-layer managing unit 120c and acquires a free block FB
together with a logical block ID allocated as the free bock FB. The
logical-NAND-layer managing unit 120b requests the
physical-NAND-layer managing unit 120c to copy a plurality of
tracks selected as compaction objects to the free block FB. When
the tracks as the compaction objects have valid clusters in the WC
21, the FS unit 12Q, and the IS unit 13Q, the logical-NAND-layer
managing unit 120b executes the passive merge for collecting and
merging the valid clusters in the MS compaction buffer 11c.
[0302] When the completion of the compaction is notified from the
physical-NAND-layer managing unit 120c, the logical-NAND-layer
managing unit 120b updates the logical block ID 30c in an entry
having the logical track addresses 30a corresponding to the tracks
subjected to the compaction of the track management table 30a to
the logical block ID of the free block FB acquired from the
physical-NAND-layer managing unit 120c and updates the
intra-logical block track position 30d.
[0303] The logical-NAND-layer managing unit 120b registers the
logical block ID of the free block FB acquired from the
physical-NAND-layer managing unit 120c, which is used as the MS
compaction buffer 11c, as a new entry in the MS logical block
management table 35 and registers required information in
respective fields in the entry. As the registration, there are
update of the track management pointer 35b, update of the number of
valid tracks, update of the writable top track 35d, and the
like.
[0304] The logical-NAND-layer managing unit 120b registers the
logical block ID used as the MS compaction buffer 11c at the top of
the FIFO structure (the linked list) of the field 61c for the TFS
of the MS buffer management table 61 of the MS structure management
buffer 60 to move the MS compaction buffer 11c configured by one
logical block including the valid 2.sup.i tracks as a result of the
MS compaction to the top (an oldest position) of the TFS 11b. When
the TFS 11b is full, an oldest logical block at the top is moved to
the MS 11.
[0305] Subsequently, the data managing unit 120 invalidates old
track at a compaction source in the MS 11. Specifically, the
logical-NAND-layer managing unit 120b deletes a relevant section of
a field of the track management pointer 35b in an entry
corresponding to a logical block at the compaction source in the MS
logical block management table 35, decrements the number of valid
tracks 35c, and updates the logical block ID list by the number of
valid tracks 62 of the MS structure management table 60. When the
number of valid tracks 35c is reduced to 0 by the decrement, the
logical-NAND-layer managing unit 120b decrements the number of
valid logical blocks VBL of the MS structure management table 60,
and returns this invalid logical block to the physical-NAND-layer
managing unit 120c. The valid flag 35e of an entry of the MS
logical block management table 35 corresponding to the returned
logical block is set invalid.
[0306] When such compaction processing and processing for returning
the invalid logical block FB are finished, the logical-NAND-layer
managing unit 120b compares the number of valid logical blocks VBL
and the maximum number of logical blocks MBL. When the number of
valid logical blocks VBL exceeds the maximum number of logical
blocks MBL, the logical-NAND-layer managing unit 120b executes the
2.sup.i track MS compaction for collecting 2.sup.i valid tracks
again. When the 2.sup.i track MS compaction for collecting 2.sup.i
valid tracks is impossible in a state in which the number of valid
logical blocks VBL exceeds the maximum number of logical blocks
MBL, the logical-NAND-layer managing unit 120b executes the less
than 2.sup.i track MS compaction.
[0307] In the less than 2.sup.i track MS compaction, the
logical-NAND-layer managing unit 120b copies tracks in a number
less than the 2.sup.i tracks as the compaction objects to the MS
additional recording IB 11ab to generates an invalid logical block
formed by the invalid 2.sup.i tracks. The logical-NAND-layer
managing unit 120b returns the generated invalid logical block to
the physical-NAND-layer managing unit 120c to reduce the number of
valid logical blocks VBL. Explanation of update of the management
tables for the less than 2.sup.i track MS compaction is
omitted.
CIB Processing in the FS 12
[0308] The CIB processing in the FS 12 explained at step S340 in
FIG. 19 is explained in detail. The logical-NAND-layer managing
unit 120b acquires information of the number of valid clusters
concerning the logical block IDs registered in the field 66a for
the FSFB and the field 66b for the FS additional recording IB of
the FS input buffer management table 66 of the FS/IS structure
management table 65 from a field of the number of valid clusters
42d of the FS/IS logical block management table 32. The
logical-NAND-layer managing unit 120b checks whether one or more
full logical blocks, in which all logical pages are written with
clusters, are present in the FSFB 12aa or the FS additional
recording IB 12ab of the FSIB 12a (step S440). When one or more
full logical blocks are present in the FSIB 12a, the
logical-NAND-layer managing unit 120b performs the processing
explained below. When the judgment at step S440 is NO, the
procedure is finished here.
[0309] When the judgment at step S440 is YES, the
logical-NAND-layer managing unit 120b checks whether an invalid
logical block, the number of valid clusters 42d of which is 0, is
present in the FS unit 12Q referring to the number of valid
clusters 42d of the FS/IS structure management table 65 and the
FS/IS logical block management table 42. When the invalid logical
block is present in the FS unit 12Q, the logical-NAND-layer
managing unit 120b returns the invalid logical block to the
physical-NAND-layer managing unit 120c (step S445).
[0310] An entry of the returned logical block is deleted from the
MS logical block management table 35 and the FS/IS logical block
management table 42. The logical-NAND-layer managing unit 120b
moves a full logical block in the FSFB 12aa to the FS 12 and moves
a full logical block in the FS additional recording IB 12ab to the
FS 12 (step S447). Specifically, the Move processing is processing
for only deleting relevant logical block IDs registered in the
field 66a for the FSFB and the field 66b for the FS additional
recording IB of the FS input buffer management table 66 of the
FS/IS structure management table 65.
[0311] The logical-NAND-layer managing unit 120b judges whether the
number of logical blocks of the FS 12 having the FIFO structure
exceeds a predetermined maximum number of logical blocks BLfsmax
allowed for the FS 12 (step S450). Specifically, the
logical-NAND-layer managing unit 120b judges whether the number of
logical blocks calculated from the FS FIFO management table 67
exceeds the maximum number of logical blocks BLfsmax set in
advance.
[0312] As a result of this comparison, when the calculated number
of logical blocks exceeds the maximum number of logical blocks
BLfsmax, the logical-NAND-layer managing unit 120b executes flush
processing for, for example, two logical blocks at a time to the MS
11 (step S460) and flush processing for one logical block to the IS
13 (step S500) according to a state at that point. When the FS 12
is not full in the judgment at step S450, the logical-NAND-layer
managing unit 120b finishes the processing here without performing
flush processing from the FS 12 to the MSIB 11a and flush
processing from the FS 12 to the ISIB 13a.
[0313] In the flush processing from the FS 12 to the MSIB 11a,
first, the logical-NAND-layer managing unit 120b judges whether
there is a logical block directly copied to the MSIB 11a without
being moved through the IS unit 13Q from the FS (step S455).
Specifically, the logical-NAND-layer managing unit 120b checks
clusters in an oldest logical block at the top of the FIFO of the
FS 12 in order one by one and searches how many valid clusters a
track to which the clusters belong has in the FS unit 12Q referring
to a field of the number of FS clusters 31f of the track management
table 30. When the number of valid clusters in the track is equal
to or larger than a predetermined threshold (e.g., 2.sup.k-i-1),
the logical-NAND-layer managing unit 120b sets the logical track
address as a track decided to be flushed to the MSIB 11a.
[0314] The search is performed through a route explained below.
[0315] 1. The logical-NAND-layer managing unit 120b obtains an
oldest FS/IS block ID at the top of the FIFO from the FS FIFO
management table 65 of the FS/IS structure management table 65.
[0316] 2. The logical-NAND-layer managing unit 120b obtains an
index to the intra-FS/IS cluster management table 44 from a field
of the intra-block cluster table 42c in an entry of the FS/IS
logical block management table 42 corresponding to the FS/IS block
ID.
[0317] 3. The logical-NAND-layer managing unit 120b obtains one
pointer to the FS/IS management table 40 from each entry in one
logical block designated by the index obtained in the intra-FS/IS
cluster management table 44 and jumps to a relevant link of the
FS/IS management table 40.
[0318] 4. The logical-NAND-layer managing unit 120b obtains a
relevant logical track address to which the link at a jump
destination belongs.
[0319] 5. The logical-NAND-layer managing unit 120b checks a field
of the number of FS clusters 30f in a relevant entry of the track
management table 30 using the obtained logical track address.
[0320] 6. The logical-NAND-layer managing unit 120b repeats 3 to 5
explained above.
[0321] The flush from the FS 12 to the MS 11 is performed for, for
example, two logical blocks at a time (block Copy). In other words,
the logical-NAND-layer managing unit 120b collects tracks having
the number of intra-track valid clusters equal to or larger than a
predetermined threshold (e.g., 2.sup.k-i-1) for two logical blocks
and flushes the collected tracks for two logical blocks to the MSFB
11aa of the MSIB 11a (step S460). In the flush, concerning clusters
not present in the FS 12 in the flushed track, the
logical-NAND-layer managing unit 120b executes the passive merge
for reading out the clusters from the WC 21, the IS unit 13Q, and
the MS 11 and merging the clusters.
[0322] However, when tracks decided to be flushed to the MSIB 11a
are not present for two logical blocks, the logical-NAND-layer
managing unit 120b flushes one logical block to the MSFB 11aa of
the MSIB 11a (block Copy) and additionally records tracks not
enough for one logical block in the MS additional recording IB 11ab
in track units (track Copy) (step S460). Similarly, when tracks
decided to be flushed to the MSIB 11a are not present for one
logical block, the logical-NAND-layer managing unit 120b
additionally records tracks not enough for one logical block in the
MS additional recording IB 11ab in track units (track Copy) (step
S460). Thereafter, when no valid cluster is left in the top logical
block of the FS 12 of the FIFO structure, the logical-NAND-layer
managing unit 120b returns the top logical block to the
physical-NAND-layer managing unit 120c as an invalid logical
block.
CIB Processing in the MS 11 (Step S350 in FIG. 19)
[0323] When the flush from the FS 12 to the MSIB 11a is performed
in this way, the CIB processing in the MS unit 11Q is again
executed (step S480). The CIB processing in the MS unit 11Q at step
S480 is the same as the CIB processing in the first time in the MS
unit 11Q (steps S400 to S420). Therefore, redundant explanation is
omitted. After the CIB processing in the MS unit 11Q, the
logical-NAND-layer managing unit 120b checks in the same manner as
explained above whether a condition for flush from the FS 12 to the
MSIB 11a is satisfied (step S455). When the flush condition is
satisfied, the flush of every two logical blocks from the FS 12 to
the MSIB 11a and the CIB processing in the MS 11 explained above is
again executed. Such processing is repeated until the judgment NO
is obtained at step S455.
CIB Processing in the FS 12
[0324] When the judgment at step S455 is NO, the logical-NAND-layer
managing unit 120b judges whether a condition for flush from the FS
12 to the ISIB 13a is satisfied (step S490). Specifically, in the
flush processing from the FS 12 to the MSIB 11a, when a valid
cluster is left in the checked top logical block of the FS 12 in a
full state having the FIFO structure, the logical-NAND-layer
managing unit 120b executes flush from the FS 12 to the ISIB 13a
assuming that condition for flush from the FS 12 to the IS 13 at
step S490 is satisfied.
[0325] When the condition is satisfied at step S490, the
logical-NAND-layer managing unit 120b moves the top logical block
including only clusters not included in the track flushed to the
MSIB 11a to the ISIB 13a (block Move) (step S500). At step S500,
the logical-NAND-layer managing unit 120b executes, for example,
flush of one logical block. Depending on a state, thereafter, after
performing the procedure at steps S520 to S585, the
logical-NAND-layer managing unit 120b may perform the flush from
the FS 12 to the ISIB 13a at step S500 again according to the
judgment at step S590.
[0326] A state in which the flush is performed again at step S500
is a state in which, for example, when a buffer (the FSFB 12a or
the FS additional recording IB 12ab) having a plurality of full
logical blocks is present in the FSIB 12a, if the FS 12 having the
FIFO structure is full, flush of a plurality of logical blocks from
the FS 12 to the MSIB 11a or the ISIB 13a is performed according to
the move of a full block from the FSIB 12a to the FS 12. Under such
a condition, it is likely that flush of a plurality of logical
blocks from the FS 12 to the ISIB 13a is performed.
CIB Processing in the IS (Step S360 in FIG. 19)
[0327] Details of flush processing and compaction processing
performed in the IS 13 when the condition at step S490 is satisfied
are explained with reference to, besides FIG. 30, a flowchart shown
in FIG. 31. First, in the same manner as explained above, the
logical-NAND-layer managing unit 120b checks whether an invalid
logical block is present in the IS unit 13Q and, when an invalid
logical block is present in the IS unit 13Q, returns the invalid
logical block to the physical-NAND-layer managing unit 120c (step
S520). In entries of the MS logical block management table 35 and
the FS/IS logical block management table 42 corresponding to an
entry of the returned logical block, the valid flags 35e and 42f
are set invalid.
[0328] The logical-NAND-layer managing unit 120b judges whether the
number of logical blocks of the IS 13 having the FIFO structure
exceeds the predetermined maximum number of logical blocks BLismax
allowed for the IS 13 (step S530). Specifically, the
logical-NAND-layer managing unit 120b judges whether the number of
logical blocks calculated from the IS FIFO management table 69
exceeds the maximum number of logical blocks BLismax set in
advance.
[0329] As a result of the comparison, when the calculated number of
logical blocks exceeds the maximum number of logical blocks
BLismax, the logical-NAND-layer managing unit 120b flushes tracks
for, for example, two logical blocks at a time from the IS 13 to
the MSFB 11aa of the MSIB 11a (step S540). When the IS 13 is not
full in the judgment at step S530, the logical-NAND-layer managing
unit 120b moves a full logical block in the ISIB 13a to the IS 13b
without performing flush processing to the MSIB 11a (step
S585).
[0330] In the flush at step S540, the logical-NAND-layer managing
unit 120b executes processing for selecting a track to be flushed
shown in FIG. 31 using the track management table 30 or the like
shown in FIG. 12. In FIG. 31, the logical-NAND-layer managing unit
120b starts the selection processing (cyclic search processing;
hereinafter simply referred to as search processing) (step S700).
The logical-NAND-layer managing unit 120b starts a search from the
next logical track address of the logical track address 30a as an
index of the track management table 30 stored at step S740 as a
final searched track in the last search (step S710).
[0331] When the search is a search for the first time (a first
cycle), the logical-NAND-layer managing unit 120b starts the search
from a first entry of the track management table 30 (step S710).
When the searched track stored at step S740 is a final entry (a
track n in FIG. 12) of the track management table 30, in the next
track search at step S710, the logical-NAND-layer managing unit
120b returns to the top entry (a track 0 in FIG. 12).
[0332] In this search, referring to a field (the number of valid
clusters in a relevant logical track address) of the number of IS
clusters 30g in the entry of the track management table 30, when a
valid cluster is stored in the entry of the IS 13, the
logical-NAND-layer managing unit 120b registers a logical track
address of the entry in a not-shown newly searched track list (step
S720). The logical-NAND-layer managing unit 120b compares the
number of tracks registered in the newly searched track list with a
predetermined threshold L. When the number of registered track is
smaller than the threshold L, the logical-NAND-layer managing unit
120b shifts the procedure to step S710 and checks the next entry of
the track management table 30 in the same manner as explained
above.
[0333] By repeating such processing, the logical-NAND-layer
managing unit 120b registers logical track addresses for the
threshold L in the newly searched track list ("Yes" at step S730).
The logical-NAND-layer managing unit 120b stores an entry (an
index) of the track management table 30 corresponding to a logical
track addresses registered in the newly searched track list last as
a searched last track and finishes the search in the present cycle
(step S740).
[0334] The logical-NAND-layer managing unit 120b judges whether
there is an unselected track list in which logical track addresses
not selected last time (not shown) are listed (step S750). In the
case of the first cycle, because the unselected track list is not
present, the logical-NAND-layer managing unit 120b selects
2.sup.i+1 logical tracks based on two lists, i.e., the newly
searched track list and newly added intra-block track list (not
shown) (step S760). The newly added intra-block track list is a
list concerning tracks included in the logical block (entered in
the IS input buffer management table 68 of the FS/IS structure
management table 65) flushed from the FS 12 to the IS unit 13Q at
step S500 in FIG. 30.
[0335] In the first cycle, the logical-NAND-layer managing unit
120b selects 2.sup.i+1 tracks as flush candidates using such two
lists. In the selection, as explained above, a selection reference
(score value) S obtained by using the number of valid clusters in
track and a valid cluster coefficient is used.
Score value S=the number of valid clusters in track.times.valid
cluster coefficient
[0336] The valid cluster coefficient is a number weighted according
to whether a track is present in a logical block in which an
invalid track is present in the MS unit 11Q. The number is larger
when the track is present than when the track is not present.
[0337] The number of valid clusters can be acquired by looking at a
field of the number of IS clusters 30g of the track management
table 30. The valid cluster coefficient can be acquired by looking
at a field of the number of valid tracks 35c of the MS logical
block management table 35 linked to the track management table 30
by a field of the track management pointer 35b.
[0338] The logical-NAND-layer managing unit 120b selects M (a
predetermined set value) tracks with larger score values S from a
plurality of tracks included in the newly added intra-block track
list. The logical-NAND-layer managing unit 120b adds L tracks
registered in the newly searched track list by the prior search to
the selected M tracks and selects 2.sup.i+1 tracks with higher
score values S from the L+M tracks as tracks to be flushed to the
MS 11. The logical-NAND-layer managing unit 120b registers tracks
other than the selected 2.sup.i+1 tracks among the L+M tracks in
the unselected track list.
[0339] In a second or subsequent cycle, the logical-NAND-layer
managing unit 120b selects 2.sup.i+1 tracks based on three lists,
i.e., the unselected track list, the newly searched track list, and
the newly added intra-block track list (step S770). It is
determined according to judgment at step S570 in FIG. 30 explained
later whether flush for a second or subsequent time should be
performed. In the selection processing using the three lists, the
logical-NAND-layer managing unit 120b selects N (a predetermined
set value) tracks with higher score values S from a plurality of
tracks included in the unselected track list, selects M (a
predetermined set value) tracks with higher score values S from a
plurality of tracks included in the newly added intra-block track
list, adds L tracks registered in the newly searched track list
obtained in the present second or subsequent cycle to the N+M
tracks, and selects 2.sup.i+1 tracks with higher score values S out
of the L+M+N tracks as tracks to be flushed to the MS 11. The
logical-NAND-layer managing unit 120b registers tracks other than
the selected 2.sup.i+1 tracks among the L+M+N logical tracks in the
unselected track list used in the next cycle.
[0340] Referring back to step S540 in FIG. 30, when the flush
candidates of the tracks for two logical blocks are selected as
explained above, the logical-NAND-layer managing unit 120b flushes
the selected tracks for two logical blocks (i.e., 2.sup.i+1 tracks)
to the MSFB 11aa of the MSIB 11a (step S540). In the flush,
concerning clusters not present in the IS unit 13Q among the tracks
to be flushed, the passive merge for reading out the clusters from
the WC 21, the FS unit 12, and the MS 11 and merging the clusters
is executed. In the above description, the tracks to be flushed are
selected according to the score value S based on the number of
valid clusters and the coefficient indicating whether porous blocks
are present in the MS. However, tracks to be flushed may be
selected according to only the number of valid clusters.
CIB Processing in the MS (Step S370 in FIG. 19)
[0341] When the flush from the IS 13 to the MSIB 11a is performed
in this way, the CIB processing in the MS 11 is again executed
(step S560). The CIB processing in the MS 11 at step S560 is the
same as the CIB processing in the MS 11 in the first time (steps
S400 to S420). Therefore, redundant explanation is omitted.
CIB Processing in the IS
[0342] The logical-NAND-layer managing unit 120b judges whether
flush from the IS 13 to the MSIB 11a should be executed again (step
S570). The logical-NAND-layer managing unit 120b sorts, using
fields of the MS logical block management table 35 and the number
of valid clusters 42d of the FS/IS logical block management table
42 and the like, logical blocks in the IS 13 after the flush at
step S540 in order from one with a smallest number of valid
clusters. When a total number of valid clusters of two logical
blocks with a smallest number of valid clusters is equal to or
larger than 2.sup.k (for one logical block), which is a
predetermined set value, the logical-NAND-layer managing unit 120b
judges that a condition for flush from the IS 13 to the MSIB 11a is
satisfied (step S570).
[0343] When the condition for flush from the IS 13 to the MSIB 11a
is satisfied, the logical-NAND-layer managing unit 120b shifts the
procedure to step S540 and executes steps S700 to S750 and S770 in
FIG. 31 to execute the flush processing for two logical blocks
explained above again. As long as the judgment at step S570 is YES,
the logical-NAND-layer managing unit 120b repeatedly executes the
flush processing for two logical blocks from the IS 13 to the MSIB
11a and the CIB processing in the MS 11. When the judgment at step
S570 is NO, the logical-NAND-layer managing unit 120b executes the
compaction processing in the IS 13 (step S580).
[0344] In the IS compaction processing, the logical-NAND-layer
managing unit 120b collects, using fields of the MS logical block
management table 35 and the number of valid clusters 42d of the
FS/IS logical block management table 42 and the like, clusters for
one logical block in order from a logical block having a smallest
number of valid clusters in the IS unit 13Q, i.e., 2.sup.k clusters
and copies the 2.sup.k clusters to the IS compaction buffer 13c.
When this copy processing is finished, the logical-NAND-layer
managing unit 120b returns logical blocks without valid clusters
among the logical blocks at a compaction source (a Copy source) to
the physical-NAND-layer managing unit 120c as invalid logical
blocks. The logical-NAND-layer managing unit 120b moves the IS
compaction buffer 13c configured by logical blocks filled with
valid clusters by the compaction processing to the IS 13.
[0345] After this compaction, full logical blocks in the ISIB 13a
is moved to the IS 13 (step S585). Specifically, this Move
processing is processing for only deleting a relevant logical block
ID registered in the field for the ISIB of the IS input buffer
management table 68 of the FS/IS structure management table 65.
[0346] Thereafter, the logical-NAND-layer managing unit 120b judges
whether the condition for flush from the FS 12 to the ISIB 13a is
satisfied (step S590). When the condition for flush from the FS 12
to the ISIB 13a is satisfied, the logical-NAND-layer managing unit
120b shifts the procedure to step S500 and repeats the procedure
again. After the IS compaction processing is finished, when it is
judged that the condition for flush from the FS 12 to the ISIB 13a
is not satisfied, the logical-NAND-layer managing unit 120b
finishes the present write processing. The above is the details of
the write processing.
[0347] As explained above, in this embodiment, the
logical-NAND-layer managing unit 120b executes the readout
processing and the write processing (WCF+CIB) for the MS unit 11Q,
the FS unit 12Q, and the IS unit 13Q as the components in the NAND
memory 10, the management in track units for the MS unit 11Q, the
management in cluster units for the FS unit 12Q and the IS unit
13Q, and the like based on the forward lookup track management
table 30 and FS/IS management table 40 and the reverse lookup MS
logical block management table 35, FS/IS logical block management
table 42, and intra-FS/IS cluster management table 44.
[0348] The forward lookup track management table 30 shown in FIG.
12 is a table for mainly managing logical data positions (the
logical block IDs 30c and the intra-logical block track positions
30d) on the MS 11 using, as an index, the logical track addresses
30a obtained by aligning, in track units, the LBAs aligned in
sector units. When data is stored in the FS unit 12Q and the IS
unit 13Q in cluster units, pointers as link information to entries
to the FS/IS management table 40, in which basic information and
detailed information concerning the data are registered, are also
stored (see A1). Information necessary for the flush processing and
the compaction processing in writing such as the numbers of FS
clusters 30f and the numbers of IS clusters 30g are stored with the
logical track addresses 30a set as indexes.
[0349] Logical cluster addresses obtained by aligning LBAs in
cluster units are used for the forward lookup FS/IS management
table 40 shown in FIG. 13. The FS/IS management table 40 is formed
in a linked list format independent for each of logical track
addresses. Each of linked lists for each of the logical track
addresses is a table for managing logical data positions (the
logical block IDs 40b+the intra-logical block cluster positions
40c) on the FS unit 12Q or the IS unit 13Q in logical cluster
address units belonging to the logical track addresses. The linked
list includes fields of the FS/IS block IDs 40d as link information
to indexes of the FS/IS logical block management table 42 (see
A5).
[0350] The reverse lookup MS logical block management table 35
shown in FIG. 14 stores, with the logical block IDs set as indexes,
the track management pointers 35b equivalent to the numbers of
tracks in the logical blocks. The reverse lookup MS logical block
management table 35 is a pointer to the indexes of the track
management table 30 (see A2) indicating which track addresses are
stored in the logical block IDs 35a. This makes it possible to
manage the logical track address belonging to each of the logical
block IDs 35a. Further, the MS logical block management table 35
stores, with the logical block IDs 35a set as indexes, information
necessary for the flush processing, the compaction processing, and
the like in writing, that is, the number of valid tracks 35c, the
writable top track 35d, the valid flag 35e, and the like.
[0351] The reverse lookup FS/IS logical block management table 42
shown in FIG. 15 is a table for managing, with the FS/IS block IDs
42a set as indexes, information indicating which logical cluster
address is stored in the logical block used as the FS unit 12Q or
the IS unit 13Q. Therefore, the FS/IS logical block management
table 42 has fields of the intra-block cluster tables 42c as
pointers (see A3) to the intra-FS/IS cluster management table 44.
The FS/IS logical block management table 42 stores, with the FS/IS
block IDs 42a set as indexes, information necessary for the flush
processing, the compaction processing, and the like in writing,
that is, the number of valid clusters 42d, the writable top page
42e, the valid flag 42f, and the like.
[0352] The reverse lookup intra-FS/IS cluster management table 44
shown in FIG. 16 is a table for managing each of cluster positions
(storage positions obtained by dividing the NAND memory 10 in
cluster units) in one logical block used as the FS unit 12Q and the
IS unit 13Q in association with entry positions on the table. In
contents of each of the entries 44a, pointers (see A4) as link
information to a list (one list in the linked lists) including the
logical cluster addresses managed by the FS/IS management table 40
are registered such that it is possible to identify which logical
cluster address are associated with the cluster positions.
[0353] In this way, in the management in the track units for the
NAND memory 10, the logical track addresses 30a as the indexes of
the track management table 30 and the fields of the track
management pointers 35b of the MS logical block management table 35
are linked to form the track management table 30 as a forward
lookup table and form the MS logical block management table 35 as a
reverse lookup table. Therefore, in the write processing, it is
possible to increase speed of the search processing for the
management tables in executing various kinds of processing such as
the flush processing, the compaction processing and table
updates.
[0354] For example, in the MS compaction processing, storage
positions of tracks change. It is necessary to change the MS
logical block management table 35 and the track management table 30
according to the change in the storage positions. In other words,
according to the change in the storage positions of the tracks, it
is necessary to change each of the fields (the track management
pointer 35b, the number of valid tracks 35c, the writable top track
position 35d, etc.) of indexes corresponding to the storage
positions of the MS logical block management table 35 and,
thereafter, change required information such as the logical block
IDs 30c and the intra-logical block track positions 30d in the
track management table 30.
[0355] Under such a situation, in this embodiment, rather than
registering the logical track addresses themselves in the fields of
the track management pointers 35b of the MS logical block
management table 35, the pointers to the indexes of the track
management table 30 are registered. Therefore, it is possible to
jump to entries of the indexes of the track management table 30
without performing search and change required information in the
entries.
[0356] On the other hand, when a relevant logical track address
itself is registered in the field of the track management pointer
35b, after work for changing each of the entries of the MS logical
block management table 35 is performed, processing for searching
for the relevant logical track address 30a has to be performed
while tracing indexes of the track management table 30 one by one.
After the search, required information in the entry of the relevant
logical track address 40a is changed. Therefore, speed of the work
for updating the management tables substantially decreases compared
with this embodiment.
[0357] In the management in the cluster unit for the NAND memory
10, the intra-block cluster table 42c of the FS/IS logical block
management table 42 is linked to the intra-FS/IS cluster management
table 44 and the entries 44a of the intra-FS/IS cluster management
table 44 and the FS/IS management table 40 are linked to form the
intra-FS/IS cluster management table 44 as a forward lookup table
and form the FS/IS logical block management table 42 and the
intra-FS/IS cluster management table 44 as reverse lookup table.
Therefore, in the write processing, it is possible to increase
speed of the search processing for the management tables in
executing various kinds of processing such as the flush processing,
the compaction processing and table updates.
[0358] For example, when the IS compaction processing is performed,
storage positions of clusters change. It is necessary to change the
FS/IS logical block management table 42, the intra-block cluster
table 42c, and the intra-FS/IS cluster management table 44
according to the change in the storage positions. In other words,
it is necessary to change each of the fields (the logical block IDs
42b, the intra-block cluster table 42c, the number of valid
clusters 42d, the writable top page 42e, etc.) of indexes
corresponding to the storage positions of the FS/IS logical block
management table 42 according to the change in the storage poisons
of the clusters, change registered data in each of the entries of
the intra-FS/IS cluster management table 44, and, thereafter,
further change required information such as the logical block ID
40b and the intra-logical block cluster position 40c in a relevant
logical cluster address of the FS/IS management table 40.
[0359] Under such a situation, in this embodiment, rather than
registering a logical cluster address in each of the entries of the
intra-FS/IS cluster management table 44, the pointer 44a (see A4)
to a list including a relevant logical cluster address managed by
the FS/IS management table 40 is registered. Therefore, it is
possible to jump to the list including the logical cluster
addresses of the FS/IS management table 40 from a relevant entry of
the intra-FS/IS cluster management table 44 and change required
information in the list. On the other hand, when a relevant logical
cluster address itself is registered in each of the entries of the
intra-FS/IS cluster management table 44, after work for changing
each of the entries of the intra-FS/IS management table 44 is
performed, processing for searching for the relevant logical
cluster address 40a has to be performed while tracing linked lists
in the FS/IS management table 40 one by one. After the search,
required information in the relevant logical track address 40a is
changed. Therefore, speed of the work for updating the management
tables substantially decreases compared with this embodiment.
[0360] In this embodiment, the track management table 30 has the
cluster table pointers 30e, which are pointers as link information
to top entries of the FS/IS management table 40. The FS/IS
management table 40 is a linked list independent for each of
logical track addresses. This makes it possible to reduce a memory
amount necessary for the management tables while increasing speed
of the search processing. For example, if the FS/IS management
table 40 for performing cluster management is a normal table
(including cluster addresses and storage positions currently
managed by cluster management) rather than the linked list, to
search for a cluster present on the FS unit 12Q or the IS unit 13Q,
in a worst case, the entire table may have to be searched through
and extremely long time may be required for the search. To increase
speed of search, it is also conceivable to prepare a table having
entries of all cluster addresses corresponding to LBA areas.
However, the size of a management tables is extremely large. On the
other hand, in this embodiment, the track management table 30
indexed by the logical track addresses has the pointers to the top
entries of the FS/IS management table 40, which is a linked list
independent for each of the logical track addresses. Therefore, it
is possible to save a memory amount required for the management
tables while increasing speed of the search processing.
[0361] In this way, in this embodiment, the forward lookup and
reverse lookup tables are provided in track and cluster units,
respectively, and these tables are linked. Therefore, it is
possible to increase speed of the search processing for the
management tables. Further, in this embodiment, the WC track
management table 24 and the FS/IS management table 40 include the
linked lists. Therefore, table update work is reduced and it is
possible to reduce a capacity of the management tables.
[0362] In other words, the present embodiment provides a memory
system that can increase speed of the search processing for the
management tables and reduce a memory amount required for creation
of the management tables.
[0363] The present invention is not limited to the embodiments
described above. Accordingly, various modifications can be made
without departing from the scope of the present invention.
[0364] Furthermore, the embodiments described above include various
constituents with inventive step. That is, various modifications of
the present invention can be made by distributing or integrating
any arbitrary disclosed constituents.
[0365] For example, various modifications of the present invention
can be made by omitting any arbitrary constituents from among all
constituents disclosed in the embodiments as long as problem to be
solved by the invention can be resolved and advantages to be
attained by the invention can be attained.
[0366] Furthermore, it is explained in the above embodiments that a
cluster size multiplied by a positive integer equal to or larger
than two equals to a logical page size. However, the present
invention is not to be thus limited.
[0367] For example, the cluster size can be the same as the logical
page size, or can be the size obtained by multiplying the logical
page size by a positive integer equal to or larger than two by
combining a plurality of logical pages.
[0368] Moreover, the cluster size can be the same as a unit of
management for a file system of OS (Operating System) that runs on
the host apparatus 1 such as a personal computer.
[0369] Furthermore, it is explained in the above embodiments that a
track size multiplied by a positive integer equal to or larger than
two equals to a logical block size. However, the present invention
is not to be thus limited.
[0370] For example, the track size can be the same as the logical
block size, or can be the size obtained by multiplying the logical
block size by a positive integer equal to or larger than two by
combining a plurality of logical blocks.
[0371] If the track size is equal to or larger than the logical
block size, MS compaction processing is not necessary. Therefore,
the TFS 11b can be omitted.
Second Embodiment
[0372] FIG. 32 shows a perspective view of an example of a personal
computer. A personal computer 1200 includes a main body 1201 and a
display unit 1202. The display unit 1202 includes a display housing
1203 and a display device 1204 accommodated in the display housing
1203.
[0373] The main body 1201 includes a chassis 1205, a keyboard 1206,
and a touch pad 1207 as a pointing device. The chassis 1205
includes a main circuit board, an ODD unit (Optical Disk Device), a
card slot, and the SSD 1100 described in the first embodiment.
[0374] The card slot is provided so as to be adjacent to the
peripheral wall of the chassis 1205. The peripheral wall has an
opening 1208 facing the card slot. A user can insert and remove an
additional device into and from the card slot from outside the
chassis 1205 through the opening 1208.
[0375] The SSD 1100 may be used instead of the prior art HDD in the
state of being mounted in the personal computer 1200 or may be used
as an additional device in the state of being inserted into the
card slot of the personal computer 1200.
[0376] FIG. 33 shows a diagram of an example of system architecture
in a personal computer. The personal computer 1200 is comprised of
CPU 1301, a north bridge 1302, a main memory 1303, a video
controller 1304, an audio controller 1305, a south bridge 1309, a
BIOS-ROM 1310, the SSD 1100 described in the first embodiment, an
ODD unit 1311, an embedded controller/keyboard controller (EC/KBC)
IC 1312, and a network controller 1313.
[0377] The CPU 1301 is a processor for controlling an operation of
the personal computer 1200, and executes an operating system (OS)
loaded from the SSD 1100 to the main memory 1303. The CPU 1301
executes these processes, when the ODD unit 1311 executes one of
reading process and writing process to an optical disk. The CPU
1301 executes a system BIOS (Basic Input Output System) stored in
the BIOS-ROM 1310. The system BIOS is a program for controlling a
hard ware of the personal computer 1200.
[0378] The north bridge 1302 is a bridge device which connects the
local bus of the CPU 1301 to the south bridge 1309. The north
bridge 1302 has a memory controller for controlling an access to
the main memory 1303. The north bridge 1302 has a function which
executes a communication between the video controller 1304 and the
audio controller 1305 through the AGP (Accelerated Graphics Port)
bus.
[0379] The main memory 1303 stores program or data temporary, and
functions as a work area of the CPU 1301. The main memory 1303 is
comprised of, for example, DRAM. The video controller 1304 is a
video reproduce controller for controlling a display unit which is
used for a display monitor (LCD) 1316 of the portable computer
1200. The Audio controller 1305 is an audio reproduce controller
for controlling a speaker of the portable computer 1200.
[0380] The south bridge 1309 controls devices connected to the LPC
(Low Pin Count) bus, and controls devices connected to the PCI
(Peripheral Component Interconnect) bus. The south bridge 1309
controls the SSD 1100 which is a memory device stored soft ware and
data, through the ATA interface.
[0381] The personal computer 1200 executes an access to the SSD
1100 in the sector unit. For example, the write command, the read
command, and the cache flash command are input through the ATA
interface. The south bridge 1309 has a function which controls the
BIOS-ROM 1310 and the ODD unit 1311.
[0382] The EC/KBC 1312 is one chip microcomputer which is
integrated on the embedded controller for controlling power supply,
and the key board controller for controlling the key board (KB)
1206 and the touch pad 1207. The EC/KBC 1312 has a function which
sets on/off of the power supply of the personal computer 1200 based
on the operation of the power button by user. The network
controller 1313 is, for example, a communication device which
executes the communication to the network, for example, the
internet.
[0383] Although the memory system in the above embodiments is
comprised as an SSD, it can be comprised as, for example, a memory
card typified by an SD.TM. card. Moreover, the memory system can be
applied not only to a personal computer but also to various
electronic devices such as a cellular phone, a PDA (Personal
Digital Assistant), a digital still camera, a digital video camera,
and a television set.
[0384] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *