U.S. patent application number 14/635919 was filed with the patent office on 2015-09-10 for method for reducing write amplification on a data carrier with overlapping data tracks and device thereof.
This patent application is currently assigned to inodyn NewMedia GmbH. The applicant listed for this patent is Lothar Pantel. Invention is credited to Lothar Pantel.
Application Number | 20150255114 14/635919 |
Document ID | / |
Family ID | 52876374 |
Filed Date | 2015-09-10 |
United States Patent
Application |
20150255114 |
Kind Code |
A1 |
Pantel; Lothar |
September 10, 2015 |
METHOD FOR REDUCING WRITE AMPLIFICATION ON A DATA CARRIER WITH
OVERLAPPING DATA TRACKS AND DEVICE THEREOF
Abstract
A novel symmetrical band is disclosed, which may be used in
connection with shingled magnetic recording (SMR) in order to
reduce write amplification (read-modify-write). Depending on the
embodiment, overlapping data tracks diverge from, or converge to
the center of each symmetrical band. Associated guard regions may
be located at the center, or at the band boundaries, and are shared
such that the excess width of a write element is caught by the
guard regions from both sides. A symmetrical band may reduce the
maximum write amplification by more than half. A hard disk
controller may maintain the number of taken or empty tracks on both
sides of each symmetrical band substantially equal at every fill
level.
Inventors: |
Pantel; Lothar;
(Neckargemuend, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pantel; Lothar |
Neckargemuend |
|
DE |
|
|
Assignee: |
inodyn NewMedia GmbH
Neckargemuend
DE
|
Family ID: |
52876374 |
Appl. No.: |
14/635919 |
Filed: |
March 2, 2015 |
Current U.S.
Class: |
360/48 |
Current CPC
Class: |
G06F 3/0619 20130101;
G11B 20/1252 20130101; G11B 2020/1238 20130101; G06F 12/10
20130101; G06F 2212/152 20130101; G06F 2003/0692 20130101; G11B
20/1217 20130101; G06F 2212/657 20130101; G06F 2212/1032 20130101;
G06F 2212/21 20130101; G06F 2212/70 20130101; G06F 11/1469
20130101; G06F 3/0676 20130101; G06F 3/064 20130101 |
International
Class: |
G11B 20/12 20060101
G11B020/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2014 |
DE |
102014003205.1 |
Claims
1. A method for reducing write amplification on a data carrier
surface with overlapping data tracks, comprising: a) writing
overlapping data tracks on said data carrier surface, establishing
a plurality of symmetrical bands with overlaps in opposite radial
directions essentially between the middle of each symmetrical band
and the band boundaries, wherein associated guard regions are
located essentially in the middle of each symmetrical band, or at
the band boundaries, wherein the excess width of data tracks,
written on both tracks adjacent to each guard region, is caught by
said guard regions from both sides, b) maintaining the number of
taken or empty tracks on both sides of each symmetrical band
substantially equal at every fill level of each symmetrical
band.
2. The method of claim 1, further comprising symmetrical bands
whose associated guard regions are located in the middle or near
the middle of each symmetrical band, both tracks adjacent to each
guard region being written such that the excess width of a write
element is caught by said guard region from both sides.
3. The method of claim 2, wherein overlapping data tracks, written
by said write element, converge from both outer boundaries of each
symmetrical band inward, toward said guard regions, establishing
overlaps in opposite radial directions within each symmetrical
band.
4. The method of claim 2, further comprising: a) writing data
substantially to the two outermost tracks on both sides of each
symmetrical band, essentially in a first filling stage, b) writing
data substantially to the next inwardly adjacent tracks on both
sides of each symmetrical band, essentially in a second filling
stage.
5. The method of claim 4, further comprising writing data
substantially to the two innermost tracks adjacent to the guard
region of each symmetrical band, essentially in a final filling
stage.
6. The method of claim 1, further comprising at least two adjacent
symmetrical bands whose shared guard region is located at the
common boundary of said symmetrical bands, the tracks adjacent to
said common boundary being written such that the excess width of a
write element is caught by said shared guard region from both
sides.
7. The method of claim 6, wherein overlapping data tracks, written
by said write element, diverge from a location in the middle or
near the middle of each symmetrical band outward, toward said
shared guard regions, establishing overlaps in opposite radial
directions within each symmetrical band.
8. The method of claim 6, further comprising: a) writing data
substantially to the two innermost tracks in the middle of each
symmetrical band, essentially in a first filling stage, b) writing
data substantially to the next outwardly adjacent tracks on both
sides of each symmetrical band, essentially in a second filling
stage.
9. The method of claim 8, further comprising writing data
substantially to the two outermost tracks on both sides of each
symmetrical band, essentially in a final filling stage, said
outermost tracks being adjacent to the shared guard regions.
10. The method of claim 1, further comprising: a) writing data
substantially to every second, third, or n-th track on both sides
of each symmetrical band, essentially in a first filling stage,
where n is a natural number greater than three, b) writing data
substantially to all remaining, empty tracks of each symmetrical
band, essentially in at least one subsequent filling stage.
11. The method of claim 1, further comprising writing frequently
changing data to tracks adjacent to said guard regions and/or
writing archive data to tracks that have an increased distance to
said guard regions within each symmetrical band.
12. The method of claim 1, wherein: a) said data carrier surface is
a disk surface of a hard disk drive that operates according to the
shingled magnetic recording methodology, b) physical sectors on
said tracks are assigned and/or remapped by means of a logical
block address mapping technique.
13. A storage device optimized for low write amplification,
comprising: a) at least one data carrier surface, b) at least one
write element whose data track width exceeds the track width of a
read element by an excess width, c) a plurality of symmetrical
bands each comprising overlapping data tracks, written by said
write element on said data carrier surface with overlaps in
opposite radial directions essentially between the middle of each
symmetrical band and the band boundaries, wherein associated guard
regions are located essentially in the middle of each symmetrical
band, or at the band boundaries, wherein the excess width of data
tracks, written on both tracks adjacent to each guard region, is
caught by said guard regions from both sides, d) a control unit
configured to maintain the number of taken or empty tracks on both
sides of each symmetrical band substantially equal at every fill
level of each symmetrical band.
14. The storage device of claim 13, further comprising symmetrical
bands whose associated guard regions are located in the middle or
near the middle of each symmetrical band, both tracks adjacent to
each guard region being written such that the excess width of said
write element is caught by said guard region from both sides.
15. The storage device of claim 14, wherein overlapping data
tracks, written by said write element, converge from both outer
boundaries of each symmetrical band inward, toward said guard
regions, establishing overlaps in opposite radial directions within
each symmetrical band.
16. The storage device of claim 14, wherein said control unit is
configured to: a) add data substantially to the two outermost
tracks on both sides of each symmetrical band, essentially in a
first filling stage, b) add data substantially to the next inwardly
adjacent tracks on both sides of each symmetrical band, essentially
in a second filling stage.
17. The storage device of claim 13, further comprising at least two
adjacent symmetrical bands whose shared guard region is located at
the common boundary of said symmetrical bands, the tracks adjacent
to said common boundary being written such that the excess width of
said write element is caught by said shared guard region from both
sides.
18. The storage device of claim 17, wherein overlapping data
tracks, written by said write element, diverge from a location in
the middle or near the middle of each symmetrical band outward,
toward said shared guard regions, establishing overlaps in opposite
radial directions within each symmetrical band.
19. The storage device of claim 17, wherein said control unit is
configured to: a) add data substantially to the two innermost
tracks in the middle of each symmetrical band, essentially in a
first filling stage, b) add data substantially to the next
outwardly adjacent tracks on both sides of each symmetrical band,
essentially in a second filling stage.
20. The storage device of claim 13, wherein: a) said storage device
is a hard disk drive that operates according to the shingled
magnetic recording methodology, b) said data carrier surface is a
disk surface of said hard disk drive, c) said control unit is a
hard disk controller of said hard disk drive, d) said control unit
is configured to assign and/or remap physical sectors on said
tracks by means of a logical block address mapping technique.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from German Patent
Application DE 10 2014 003 205.1, filed Mar. 4, 2014, the entire
disclosure of which is expressly incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to the field of data storage
and, in particular, to efficient write operations in conjunction
with storage devices having overlapping data tracks, such as a hard
disk drive, operating according to the shingled magnetic recording
(SMR) methodology.
BACKGROUND OF THE INVENTION
[0003] Common hard disk drives are storage devices comprising disks
whose data-carrying surfaces are coated with a magnetic layer.
Typically, the disks are positioned atop one another on a disk
stack (platters) and rotate around an axis, or spindle. To store
data, each disk surface is organized in a plurality of circular,
concentric tracks. Groups of concentric tracks placed atop each
other in the disk stack are called cylinders. Read/write heads,
each containing a read element and a write element, are mounted on
an actuator arm and are moved over the spinning disks to a selected
track, where the data transfer occurs. The actuator arm is
controlled by a hard disk controller, an internal logic responsible
for read and write access. A hard disk drive can perform random
read and write operations, meaning that small amounts of data are
read and written at distributed locations on the various disk
surfaces.
[0004] Each track on a disk surface is divided into sections, or
segments, known as physical sectors. A physical sector, also
referred to as a data block or sector data, typically stores a data
unit of 512 bytes or 4 KB of user data.
[0005] A disk surface may be divided into zones. Zones are regions
wherein each track comprises the same number of physical sectors.
From the outside inward, the number of physical sectors per track
may decrease from zone to zone. This approach is known as zone bit
recording.
[0006] A computer, or host, accessing a hard disk drive may use
logical block addresses (LBAs) in commands to read and write sector
data without regard for the actual locations of the physical
sectors on the disc surfaces. By means of a hard disk controller
the logical block addresses (LBAs) can be mapped to physical block
addresses (PBAs) representing the physical locations of sector
data. Different mapping techniques for an indirect LBA-to-PBA read
and write access are known in the prior art. In some embodiments
LBA-to-PBA mapping does not change often. In other embodiments the
LBA-to-PBA mapping may change with every write operation, the
physical sectors being assigned dynamically.
[0007] The storage capacity of a hard disk drive can be increased,
inter alia, by reducing the track pitch (i.e., track width) of the
concentric tracks on the disk surfaces. This requires a decrease in
the size of the read and write elements. However, without new
storage technologies, a reduction in the size of the write elements
is questionable, as the magnetic field that can be generated is
otherwise too small to adequately magnetize the individual bits on
the disk surface. A known solution is the shingled magnetic
recording methodology, by which a write element writes data tracks
in an overlapping fashion. Further information pertaining to
shingled magnetic recording (SMR) can be found in patents U.S. Pat.
No. 8,223,458 B2 and U.S. Pat. No. 8,432,633 B2, as well as in
patent applications US2013/0170061 A1, US2007/0183071 A1 and
US2012/0233432 A1.
[0008] With SMR, overlapping data tracks are grouped into bands,
which are separated by inter-band gaps, also known as "guard
bands," "guard regions," or "guard tracks." Typically, to change
the contents of a first track in an already populated band, it is
necessary to read out and buffer all subsequent tracks of the band.
After updating the data on that first track, rewriting the entire
buffered data up to the next guard region typically is unavoidable
because the wide write element will inevitably destroy each
subsequent track. Due to the sequential and overlapping structure
of SMR, even a small change to the contents stored in a band can
result in a significant increase in the amount of data that must be
read and written, thus leading to significant delays. Such a
process is referred to as "read-modify-write" or "write
amplification."
[0009] Workloads such as databases often generate random write
operations characterized by ongoing updates of small data blocks.
These are the most expensive operations within an SMR storage
system due to their significant write amplification, which
negatively impacts performance. Moreover, increasing file and data
fragmentation can slow an SMR hard disk drive much more than it can
a conventional hard-disk drive. For these reasons, SMR hard disk
drives are primarily intended for cold-storage applications, that
is, for scenarios in which data are rarely altered. In the prior
art SMR hard disk drives are deemed unsuitable as equal, universal
substitutes for conventional hard disk drives.
[0010] Known solutions for such write-amplification reductions have
their disadvantages. One option is to buffer the data of incoming
write commands and write the data in larger, contiguous blocks at a
later stage. This only works as long as the average data throughput
of the collected random write operations is sufficiently low. If
the required data throughput is permanently too high for the low
write performance of an SMR hard disk drive, even a large buffer
will run over, leading to a drastic drop in performance.
Furthermore, depending on the design, an additional and/or larger
buffer, e.g., flash memory, can increase the production costs of an
SMR hard disk drive.
[0011] Other known approaches for reducing write amplification
include garbage collection, as is also used in solid state disks
(SSDs). In contrast to conventional hard disk drives, the
association between logical block addresses (LBAs) and physical
block addresses (PBAs) is entirely mutable. A translation layer
provides a link between LBAs and PBAs. The garbage collection may
perform an internal "scrubbing" or other housekeeping tasks from
time to time by moving data internally.
[0012] U.S. Pat. No. 7,443,625 B2, entitled "Magnetic disk drive,"
describes a process that uses a "shift address table". An internal
"scrubbing" takes place at regular intervals during which the table
is "cleaned up." Patent application US2007/0174582 A1, entitled
"Mutable association of a set of logical block addresses to a band
of physical storage blocks," describes how to reduce write
amplification by means of mutable mapping between logical block
addresses and physical sectors. During regular operation stored
data can be moved to a different physical location, thereby
changing the LBA-to-PBA association. A map or table is used to
maintain the allocation or association status of each physical
sector. The disclosure of this patent application is hereby
incorporated by reference in its entirety.
SUMMARY OF THE INVENTION
[0013] Aspects of the present disclosure are directed to storage
devices with at least one data carrier surface and at least one
write element whose data track width exceeds the track width of a
read element by an excess width, such as a hard disk drive
operating according to the shingled magnetic recording
methodology.
[0014] A novel symmetrical band is disclosed, which may reduce
write amplification. Depending on the embodiment, overlapping data
tracks diverge from, or converge to the center of each symmetrical
band, establishing overlaps in opposite radial directions within
each symmetrical band. Associated guard regions may be located at
the center, near the center, or at the band boundaries, and are
shared such that the excess width of the write element is caught by
the guard regions from both sides.
[0015] Symmetrical bands may reduce write amplification, as the
number of tracks that must be updated via read-modify-write
typically is at least halved. A control unit, e.g., a hard disk
controller, may maintain the number of taken or empty tracks on
both sides of each symmetrical band substantially equal at every
fill level of each symmetrical band.
[0016] The aforementioned and many further aspects, variants,
objectives, and advantages of the invention will be comprehensible
to those skilled in the art after reading detailed descriptions of
the embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Further features, advantages, and potential applications
will be apparent from the drawings. All described and/or
illustrated features, alone or in any combination, independent of
the synopsis in individual claims, constitute the subject matter of
the invention.
[0018] FIG. 1 shows a hard disk drive.
[0019] FIG. 2 illustrates the disk stack of the hard disk drive in
profile.
[0020] FIG. 3 is an illustration of a conventional band with
overlapping data tracks.
[0021] FIG. 4 shows a symmetrical band whose guard region is
located in the middle of the band. (first embodiment)
[0022] FIG. 5 illustrates how to read data from a track in the
symmetrical band. (first embodiment)
[0023] FIG. 6 shows a symmetrical band whose guard regions are
located at the band boundaries. (second embodiment)
[0024] FIG. 7 shows the end of a first filling stage; 50% of disk
capacity is used; the guard regions are located in the middle of
each band. (third embodiment)
[0025] FIG. 8 shows the end of a second filling stage; disk full;
the guard regions are located in the middle of each band. (third
embodiment)
[0026] FIG. 9 shows the end of a second filling stage; disk full;
the guard regions are located at the band boundaries. (fourth
embodiment)
[0027] FIG. 10 shows the end of a first filling stage; 60% of disk
capacity is used; the guard regions are located in the middle of
each band. (fifth embodiment)
[0028] FIG. 11 shows the end of a second filling stage; 80% of disk
capacity is used; the guard regions are located in the middle of
each band. (fifth embodiment)
[0029] FIG. 12 shows the end of a third filling stage; disk full;
the guard regions are located in the middle of each band. (fifth
embodiment)
[0030] FIG. 13 shows the end of a first filling stage; 20% of disk
capacity is used; the guard regions are located in the middle of
each band. (sixth embodiment)
[0031] FIG. 14 shows the end of a second filling stage; 40% of disk
capacity is used; the guard regions are located in the middle of
each band. (sixth embodiment)
[0032] FIG. 15 shows the end of a fifth filling stage; disk full;
the guard regions are located in the middle of each band. (sixth
embodiment)
[0033] FIG. 16 shows the end of a first filling stage; 50% of disk
capacity is used; the guard regions are located in the middle of
each band. (seventh embodiment)
[0034] FIG. 17 shows the end of a second filling stage; 75% of disk
capacity is used; the guard regions are located in the middle of
each band. (seventh embodiment)
[0035] FIG. 18 shows the end of a third filling stage; disk full;
the guard regions are located in the middle of each band. (seventh
embodiment)
DETAILED DESCRIPTION OF THE INVENTION
[0036] FIG. 1 shows a SMR hard disk drive 1 as an example of a
storage device. The disks, with magnetic layers on their disk
surfaces 2, spin around the rotational axis of the spindle 6, upon
which the individual disks are mounted. Tracks 3 on the disk
surfaces 2 are divided into sections, or segments, referred to
herein as physical sectors 4, or sectors 4.
[0037] To perform read and write operations, the read/write heads 8
are shifted by an actuator arm to the desired track 3. The actuator
arm is moved by an actuator 7, typically a voice coil motor (VCM).
The actuator 7 is controlled by a hard disk controller 10. The hard
disk controller 10 communicates with a host system 9 and has access
to a memory, or cache 11. The memory, or cache 11 may, inter alia,
buffer data of tracks 3 or sectors 4.
[0038] FIG. 2 shows a side view of a disk stack 13 (platters),
which in this example, comprises three disks, or six disk surfaces
2, as each disk, having upper and lower sides, has two magnetic
layers. Cylinder 12 encompasses all concentric tracks 3 that are
atop each other in the disk stack 13.
[0039] A host system 9, which accesses the SMR hard disk drive 1,
may use logical block addresses (LBAs) in commands to read and
write sector data without regard for the actual locations of the
physical sectors 4 on the disc surfaces 2. LBAs may be mapped to
physical block addresses (PBAs) representing the physical sectors
4, that is, the host system 9 may target a specific physical sector
4 using a sequential LBA number, and the conversion to the physical
location (cylinder/head/sector) may be performed by the hard disk
controller 10. In this process, the geometry of the SMR hard disk
drive 1 must be taken into account, such as zones (zone bit
recording) and the number of disc surfaces 2.
[0040] Different mapping techniques for such an indirect read and
write access are known in the prior art. In some embodiments,
LBA-to-PBA mapping does not change often. In other embodiments,
LBA-to-PBA mapping may change with every write operation as the
physical sectors 4 are assigned dynamically. For instance, patent
application US2007/0174582 A1, mentioned above, describes such a
dynamic association. It is to be explicitly noted that embodiments
of the present invention can be implemented using any type of
mapping technique, including, but not limited to, dynamic or
mutable association of logical block addresses to physical sectors
4.
[0041] For shingled magnetic recording, the tracks 3 on the disk
surfaces 2 are grouped in bands 15. This is demonstrated in FIG. 3,
which shows an enlarged, sectional view of a conventional band 15,
comprising eight tracks 3. In the present disclosure, the tracks 3
are numbered by means of track numbers according to the scheme
"track #101," "track #102," "track #103," etc. The band 15,
consisting of tracks 3 from track #101 through track #108, can be
located at any suitable position on a disk surface 2.
[0042] The read/write head 8 comprises a write element 16 and a
read element 17. In accordance with the principle of shingled
magnetic recording, the width of the write element 16 exceeds the
width of the read element 17 by an excess width 18. In the
particular example, as per FIG. 3, the write element 16 is twice as
wide as the read element 17. The arrow 19 indicates the relative
direction of motion of the read/write head 8. The write element 16
writes overlapping data tracks 20, which are depicted with a
pattern. For illustrative purposes, two different patterns are used
to make the overlapping data tracks 20 more distinguishable.
Moreover, in the drawings, the sectional view of the data tracks 20
is shown slightly offset along the writing direction 19 so that the
overlapping structure is visible. Actual data tracks 20 continue in
both directions along their respective tracks 3.
[0043] Typically, in order to fill a band 15 with data, the write
element 16 starts at track #101, that is, the wide write element 16
is positioned on track pair (#101, #102). Next, to get overlapping
data tracks 20, the write element 16 is positioned on track pair
(#102, #103), etc. By overlapping the data tracks 20, the resulting
track width 5 is halved in this case.
[0044] Individual bands 15 are separated by inter-band gaps,
referred to herein as guard regions 14. FIG. 3 shows a guard region
14 on track #109, marked with a dot pattern. In the illustrated
configuration, the guard region 14 occupies a single track 3,
referred to herein as a guard track 14. In other embodiments,
depending on the excess width 18 of the write element 16, the width
of the guard region 14 may also be greater, for example, a multiple
of the track width 5.
[0045] The guard track 14 is required to close off and delimit the
band 15 so that the wide write element 16 does not overwrite any
tracks 3 of a subsequent band 15. For instance, to write data on
track #108, as shown in FIG. 3, the wide write element 16 is
positioned on track pair (#108, #109).
[0046] Those skilled in the art will recognize that, if data on the
first track 3 of the band 15 (track #101) are to be altered or
rewritten, the data on all subsequent tracks 3 up to the guard
track 14 must first be read and buffered at a temporary location or
in a memory or cache 11, and must finally be rewritten, as the
contents of each subsequent track 3 will be destroyed during the
writing process. This is referred to as read-modify-write or write
amplification.
[0047] The definition of track width 5 in shingled magnetic
recording, as used in the present disclosure, is based on the width
of the remaining readable data track 20 after overlapping with an
adjacent data track 20. This remaining readable data track 20
constitutes the track 3 for which the read element 17 is designed
or optimized.
[0048] Physical sectors 4 are sections of a track 3. The terms
"sector" and "track" are therefore closely related technically and,
depending on the desired embodiment, often equally applicable.
Commonly, the umbrella term "track" is also representative of a
portion of the track 3 under consideration. Whenever a track 3 is
mentioned in the present disclosure, it can also refer to a
physical sector 4 that is situated on it. Conversely, if the term
"physical sector" is mentioned, the relevant operation may
alternatively be applied to the entire track 3, or larger parts of
the track 3.
[0049] The terms "track" (or "track number") and "cylinder" (or
"cylinder number") are likewise closely related technically.
Whenever a process is said to take place on a track 3, this may
also concern the associated cylinder 12. Conversely, if the term
"cylinder" is mentioned, this may imply involvement of at least one
of the tracks 3 on the specified cylinder 12.
[0050] If a track 3 or band 15, 21, 22 is referred to as
"preceding," "above," "upwards," or at an "upper" location, what is
meant is that this track 3 or band 15, 21, 22 may be located
farther outside on the disk surface 2 and/or may have a smaller
track or cylinder number. If a track 3 or band 15, 21, 22 is
"succeeding," "below," "downwards," or at a "lower" location, this
track 3 or band 15, 21, 22 may be located farther inside on the
disk surface 2 and/or may have a greater track or cylinder number.
Depending on the embodiment, a reverse orientation (e.g., farther
inside instead of farther outside) or a numbering of the tracks 3
and cylinders 12 in the opposite direction may also apply.
[0051] In the present disclosure, the term "guard region" is used
as an umbrella term for "guard track." A guard track is defined as
a guard region consisting of one track 3. As a general term, a
guard region may consist of just one track 3 or more than one track
3. Depending on the embodiment, a guard region or guard track may
be defined as an integral part of the band 21 or may be defined as
a separate instance between two bands 15, 22.
[0052] FIG. 4 and FIG. 5 show a first embodiment, introducing a
novel band type for shingled magnetic recording, referred to herein
as a symmetrical band 21. A symmetrical band 21 differs from a
conventional band 15 in the position of the guard region 14, which
is located in or near the middle of the band 21. For structural
reasons, the guard region 14 in this case is defined as an integral
part of the band 21. A plurality of symmetrical bands 21 can be
arranged side-by-side without necessitating an additional gap exist
between the band boundaries.
[0053] In the specific example shown in FIG. 4 the read/write head
8 and the number of tracks 3 per band 21 correspond to the previous
example of a conventional band 15, that is, the write element 16
writes data tracks 20 that are twice as wide as the underlying
track width 5, and the band 21 contains eight tracks 3 that can be
used to store data. However, in this case, the guard track 14 is
located on track #105 and, thus, in the middle of the band 21.
[0054] In the case of a symmetrical band 21, the overlapping data
tracks 20 may be written on both sides of the band 21, from the
outside inward. This results in overlaps in opposite radial
directions, symmetrically to the guard region 14. In FIG. 4, the
overlapping data tracks 20 show the order in which the individual
tracks 3 in the band 21 may be written by the write element 16 to
fill the band 21 with data. By way of example, track #101 at the
upper band boundary may be written first; next, track #109 at the
lower band boundary, then track #102 in the upper half of the band
21, then track #108 in the lower half of the band 21, etc.
[0055] The excess width 18 of the write element 16 should always be
positioned toward the center of the band 21 so that outer tracks 3
of the band 21, which already contain valid data, cannot be
destroyed. When writing data on the two innermost tracks 3 of the
band 21 (tracks #104 and #106 as per FIG. 4), it is crucial that
the write element 16 be positioned such that the excess width 18 is
caught by the guard region 14 in both cases. In contrast to that of
a conventional band 15 (as per FIG. 3), the guard region 14 of a
symmetrical band 21 (as per FIG. 4) is used from both sides of the
band 21, that is, the two innermost tracks 3 of the band 21 share a
common guard region 14.
[0056] In this context, the term "excess width 18 of write element
16" is to be interpreted regardless of the position of the read
element 17 within the read/write head 8 and regardless of the
corresponding arrow 18 depicted in FIG. 4. E.g., the excess width
18 may be located on either sides of the write element 16,
depending on whether the write element 16 writes to a track 3 in
the upper or lower half of a band 21.
[0057] With continued reference to the situation depicted in FIG.
4, a data track 20 with valid data has been written to track pair
(#104, #105) by the wide write element 16. However, since the
contents of the guard track 14 on track #105 are irrelevant, the
guard track 14 can be overwritten while writing new data on the
lower adjacent track #106, that is, the write element 16 is
positioned on track pair (#105, #106), as shown in the drawing.
[0058] Compared with the conventional arrangement of tracks 3 in a
band 15 (as per FIG. 3), the symmetrical arrangement (as per FIG.
4) reduces the maximum write amplification by more than half. E.g.,
if data are to be changed on the first track 3 (track #101) of the
band 21, data of merely three additional tracks 3 need to be read
and rewritten, rather than of seven additional tracks 3. This
results in significantly reducing the time required to update data
in a full band 21. The average transfer rate for random write
operations is therefore increased.
[0059] FIG. 5 shows by way of example how track #102 can be read
from a full symmetrical band 21. The read/write head 8 is
positioned so that the active read element 17 is located on track
#102. The relative direction of motion of the read/write head 8 is
indicated with an arrow 19. The read element 17 fits to the width
of the tracks 3, i.e., the read element 17 is designed and
optimized for the track width 5. This also applies to the effective
width of the write element 16, which is designed to write data
tracks 20 that are twice the track width 5.
[0060] The symmetrical overlaps of data tracks 20 within a band 21
may also be arranged in the opposite direction. In this case, the
overlapping data tracks 20 may diverge in the middle of the band 22
or at a location near the middle, and the guard regions 14 may be
located at the upper and lower band boundaries. This second
embodiment is illustrated in FIG. 6. Here, the overlapping data
tracks 20 diverge between tracks #104 and #105 and the guard tracks
14 are located at the band boundaries on track #100 and #109. In
this context, the guard regions or guard tracks 14 are defined as
separate instances and are not embedded within the band 22, as each
guard region or guard track 14 may also be used by an adjacent band
22.
[0061] To fill the band 22 with data, overlapping data tracks 20
may be written by the wide write element 16 on both sides of the
symmetrical band 22 from the inside out. This may result in
overlaps in opposite radial directions, symmetrical to the center
of the band 22. By way of example, as per FIG. 6, track #104 just
above the middle of the band 22 may be written first; next, track
#105 just below the middle of the band 22, then track #103 in the
upper half of the band 22, then track #106 in the lower half of the
band 22, etc. The excess width 18 of the write element 16 may
always be positioned toward the outside of the band 22, that is,
toward the guard regions 14, so that the inner tracks 3 of the band
22, which may already contain valid data, cannot be destroyed.
[0062] FIG. 7 and FIG. 8 show a third embodiment. As in the
previous examples, a read/write head 8 is used whose write element
16 writes data tracks 20 that are twice as wide as the track width
5. Tracks 3 are grouped into symmetrical bands 21, each comprising
four usable tracks 3 and one guard track 14 at the center. In this
example, a disk surface 2 incorporates 995 tracks, counted from
track #000 to track #994, grouped into 199 bands.
[0063] For the sake of clarity and to keep the drawings manageable,
each disk surface 2 in this embodiment has a very low track count.
It is to be expressly noted that actual embodiments may have much
larger track counts. Furthermore, it is pointed out that some
parts, regions, or sections of the disk surface 2 may be used or
reserved for other purposes. It should also be noted that the
drawings represent only one disk surface 2. Further disk surfaces
2, if any, may be filled in the same manner.
[0064] The drawings illustrate how the tracks 3 of the SMR hard
disk drive 1 can be gradually filled in phases or filling stages.
Filling stages are to be understood as an instructive aid for
illustrating a typical filling sequence. Furthermore, for the sake
of simplicity, it is assumed here that initially the SMR hard disk
drive 1 is empty and/or formatted.
[0065] FIG. 7 shows a disk surface 2 at the end of the first
filling stage. The outer tracks 3 of each band 21 are taken,
resulting in a disk surface 2 wherein 50% of available capacity is
used. This filling stage may have been achieved as follows.
[0066] The host system 9 starts to issue write commands. The new
data may be added to track #000 in the 1st band. To write the new
data to this track 3, the wide write element 16 is positioned on
track pair (#000, #001). Subsequently, new data may be added to
track #004: the write element 16 is positioned on track pair (#003,
#004). The excess width 18 of the write element 16 is always
oriented toward the center of the band 21. As soon as the two outer
tracks 3 of the 1st band are filled, the process is continued in
the 2nd band: as shown in FIG. 7, a data track 20 has been written
to track pair (#005, #006), etc. While continuously filling the SMR
hard disk drive 1 with data, the read/write head 8 performs short
seeks to nearby tracks 3, that is, the settle-time may
dominate.
[0067] Depending on the embodiment, a flag for each physical sector
4 or track 3 may be managed by the hard disk controller 10,
indicating whether a physical sector 4 or track 3 is taken, i.e.,
whether the physical sector 4 or track 3 contains valid data. As
soon as data are written to a physical sector 4 or track 3, the
corresponding flag may be set, as indicated with value "1" in the
"Taken" column in FIG. 7. At the end of the first filling stage
substantially all "Taken" flags for the outer tracks 3 of the bands
21 may be set to "1", while the "Taken" flags for the inner tracks
3 retain the value "0".
[0068] Optionally, depending on the embodiment, the host system 9
may send a command indicating that a particular physical sector 4
or track 3 no longer contains valid data, such as a TRIM command as
defined in ATA specifications. Thereupon, the corresponding "Taken"
flag may be reset to zero.
[0069] In the third embodiment, when filling an empty SMR hard disk
drive 1 consisting of several disk surfaces 2, new data may
initially be written to a first disk surface 2: track pair (#000,
#001), track pair (#003, #004), track pair (#005, #006), etc.,
until the first disk surface 2 is half-full, as shown in FIG. 7.
Only then a switch of the read/write heads 8 to the next, yet
empty, disk surface 2 in the disk stack 13 takes place. The second
disk surface 2 and all subsequent disk surfaces 2 may be filled in
a similar manner until 50% of the entire capacity of the SMR hard
disk drive 1 is used.
[0070] As long as less than 50% of the capacity is used, that is,
less than 50% of all tracks 3 are taken, the written data tracks 20
will not overlap, as shown in FIG. 7. Hence, overwriting a track 3
does not require the system to read, buffer and rewrite any
adjacent tracks 3, that is, any data stored on the SMR hard disk
drive 1 can be updated without necessitating read-modify-write
operations. There is no write amplification. Below a fill level of
50% the SMR hard disk drive 1 may therefore achieve a performance
roughly equivalent to a conventional hard disk drive, even in the
case of random write operations. In many typical application
scenarios only a portion of the available capacity is used for a
long time.
[0071] With continued reference to the idealized situation shown in
FIG. 7, as soon as data are written to track pair (#993, #994) on
the last disk surface 2, the corresponding first filling stage may
be concluded. At this point, the read/write heads 8 may switch back
to the first disk surface 2. Subsequently, in a second filling
stage, the SMR hard disk drive 1 may write data to the two
innermost tracks 3 of each band 21, that is, the tracks 3 adjacent
to the guard tracks 14. As with the first filling stage,
corresponding "Taken" flags may be set to "1" as soon as valid data
are written to a physical sector 4 or track 3.
[0072] FIG. 8 shows the second filling stage. Here the wide write
element 16 may write data tracks 20, inter alia, to track pair
(#001, #002) and track pair (#002, #003) in the 1st band. The
excess width 18 of the write element 16 is caught by the guard
track 14 on track #002. As the contents stored on the guard track
14 are irrelevant, the guard track 14 can be overwritten from both
sides. The first disk surface 2 is full as soon as data have been
written to track pair (#992, #993), that is, all tracks 3 of the
first disk surface 2 are taken, as illustrated in FIG. 8. Depending
on the number of disk surfaces 2 in the disk stack 13, the process
may be repeated on the remaining disk surfaces 2 until the entire
SMR hard disk drive 1 is full.
[0073] In order to enable random write operations at any time, when
updating or writing data to an outer track 3 of a band 21, it may
be necessary to check whether valid data are already located on the
adjacent, inner track 3. In such cases, the "Taken" flags for the
inner track 3 may be evaluated before writing data. If the
corresponding flag of an adjacent inner physical sector 4 or track
3 is set to "1", a read-modify-write operation may be necessary to
prevent the wide write element 16 from overwriting valid data. For
example, before writing data to track #000, it may be necessary to
check whether valid data already exist on the inner, adjacent track
#001. If the corresponding "Taken" flag is set to "1", the sector
data on track #001 must be read and buffered, and must be rewritten
after updating or changing sector data on track #000. Otherwise, if
the flag is set to "0", the outer track #000 can be written without
read-modify-write by directly positioning the write element 16 on
track pair (#000, #001).
[0074] With regard to the worst-case scenario of random write
operations when the SMR hard disk drive 1 is full, there are two
innermost tracks 3 per band 21 that can be directly overwritten at
any time, and there are two tracks 3 at the band boundaries that
require a read-modify-write operation. Statistically, 50% of the
random write operations can be performed immediately, and for the
remaining 50%, merely a single track 3 must be buffered via
read-modify-write. Consequently, even in a worst-case scenario, the
performance of the third embodiment is reasonably competitive. If
75% of the capacity of the SMR hard disk drive 1 is used, the
probability that a random write operation can update existing data
without read-modify-write is 66.6%. The lower the fill level, the
more favorable the percentage ratio.
[0075] The third embodiment and further embodiments are
characterized by the feature that newly or recently added data can
be altered instantly, that is, without write amplification. This
applies regardless of the current fill level of the SMR hard disk
drive 1. This feature is based on the special order in which the
tracks 3 are written. The order ensures that newly or recently
written data tracks 20 are retained at their full width for as long
as possible before they are partially overwritten by adjacent data
tracks 20. The embodiments therefore take into account that newly
or recently added data are generally changed more often than old
data.
[0076] FIG. 9 shows a fourth embodiment, which is similar to the
third embodiment except that the overlaps of the data tracks 20 are
aligned in the opposite direction. Analogous to the depiction in
FIG. 6, the overlapping data tracks 20 diverge in the middle of the
bands 22, whereas the guard tracks 14 are located between the bands
22. The two inner-most tracks 3 in each band 22 are written in a
first filling stage, whereas the outer tracks 3 in each band 22 are
written in a second filling stage. The disk surface 2, as depicted
in FIG. 9, is completely filled, that is, all tracks 3 are taken.
This corresponds to the situation depicted in FIG. 8 (third
embodiment).
[0077] The "inverted" arrangement of overlapping data tracks 20, as
per FIG. 9, has a comparable performance to the arrangement in the
third embodiment and is therefore equally preferable. Further
embodiments characterized by an "inverted" arrangement of
overlapping data tracks 20 are omitted solely to keep the number of
drawings manageable.
[0078] FIG. 10 through FIG. 12 show a fifth embodiment. The
effective track width of the write element 16 is twice the track
width 5 of the read element 17. Symmetrical bands 21 are used whose
guard tracks 14 are located in the middle of the bands 21. Each
band 21 comprises eleven tracks 3, ten of which can be used for
data storage. In the present example, a disk surface 2 contains 990
tracks, counted from track #000 to track #989, grouped into 90
bands. Whether a physical sector 4 or track 3 contains valid data
is indicated in the "Taken" column. In the fifth embodiment,
filling an empty SMR hard disk drive 1 takes place in three phases
or filling stages, referred to herein as "first filling stage,"
"second filling stage," and "third filling stage."
[0079] FIG. 10 shows a disk surface 2 at the end of the first
filling stage, the point reached when 60% of the tracks 3 on each
disk surface 2 in the disk stack 13 are used. Six of ten available
tracks 3 per band 21 are taken, as indicated in the "Taken" column.
It can be seen that data have been written such that the resulting
data tracks 20 do no overlap, with the exception of the guard
tracks 14. For example, in the 1st band, data may be written to
track pair (#000, #001), track pair (#002, #003), and track pair
(#004, #005). Since the guard track 14 on track #005 can catch the
excess width 18 of the write element 16 from both sides, data
tracks 20 can also be written on track pair (#005, #006), track
pair (#007, #008), and track pair (#009, #010). While continuously
filling the SMR hard disk drive 1 with data, the read/write head 8
performs short seeks to nearby tracks 3, that is, the settle-time
may dominate.
[0080] Typically, no read-modify-write is required during the first
filling stage (i.e., up to a fill level of 60%). Even if existing
data are updated (e.g., random write operations) no write
amplification may occur, since the data tracks 20 do not overlap.
Thus, in the first filling stage, the characteristics and
performance of the SMR hard disk drive 1 may correspond to that of
a conventional hard disk drive (non-SMR).
[0081] When 60% of the tracks 3 on all disk surfaces 2 are taken
(six tracks 3 per band 21), the end of the first filling stage is
reached. At this point the second filling stage may begin, and the
read/write heads 8 may switch back from the last disk surface 2 to
the first disk surface 2.
[0082] FIG. 11 shows a disk surface 2 at the end of the second
filling stage, which is reached when 80% of the tracks 3 on each
disk surface 2 in the disk stack 13 are used. Eight of ten
available tracks 3 per band 21 are taken, as indicated in the
"Taken" column. It can be seen that data have been added to tracks
3 that are chosen in such a way that from the still unused tracks 3
those two tracks 3 are selected per band 21 that are located as
close as possible to the guard track 14. This is done to reduce the
write amplification. When adding new data, it may be sufficient to
perform a read-modify-write operation for a single track 3 (the
innermost track 3 adjacent to the guard track 14).
[0083] By way of example, with continued reference to FIG. 11, data
have been added to track #003 and track #007 in the 1st band. In
order to write data to these tracks 3, read-modify-write operations
may be required, since the wide write element 16 must write data
tracks 20 on track pair (#003, #004) and track pair (#006, #007),
the tracks #004 and #006 already being taken.
[0084] When 80% of the tracks 3 on all disk surfaces 2 are taken
(eight tracks 3 per band 21), the end of the second filling stage
is reached. At this point the third and final filling stage may
begin, and the read/write heads 8 may switch back from the last
disk surface 2 to the first disk surface 2.
[0085] FIG. 12 shows the tracks 3 of a full disk surface 2 at the
end of the third filling stage. Data are added to the last free
tracks 3 in each band 21 (e.g., track #001 and track #009 in the
1st band). This gives rise to increased write amplification, as it
may be necessary to carry out read-modify-write operations for
three additional tracks 3 when writing data to the remaining free
tracks 3. The last 20% of storage capacity of the SMR hard disk
drive 1 thus may constitute a reserve capacity that can be used
with reduced, but practicable performance.
[0086] FIG. 13 through FIG. 15 show a sixth embodiment, which
corresponds to the fifth embodiment with regard to the number of
tracks 3, number of bands 21, capacity, and read/write heads 8.
However, in contrast to the fifth embodiment, a different strategy,
that is, a different order is used to write data to the tracks 3 of
the bands 21. For purposes of illustration, an empty SMR hard disk
drive 1 is filled in five phases or filling stages, two tracks 3
per band 21 being added in each filling stage.
[0087] In the first filling stage, shown in FIG. 13, data are added
to the two outer tracks 3 of each band 21. By way of example, data
are added to track #000 and track #010 in the 1st band by writing
data tracks 20 on track pair (#000, #001) and track pair (#009,
#010). The first filling stage may correspond to the first 20% of
the hard disk drive capacity. There is no write amplification.
[0088] FIG. 14 shows the second filling stage, which may correspond
to a fill level between 20% and 40%. Data are added to the inwardly
adjacent tracks 3. For example, data may be added to track #001 and
track #009 in the 1st band by writing data tracks 20 to track pair
(#001, #002) and track pair (#008, #009).
[0089] As shown by the occupancy of the bands 21 in FIG. 14, no
write amplification occurs when adding new data or when changes are
made to the last 20% of newly added data. This is true at every
fill level. For example, at a fill level of 30%, the last 20% of
newly added data (including such data that have been added during
the first filling stage) can be changed right away, without
necessitating read-modify-write operations. This can be explained
by the fact that at every fill level, there are exactly two tracks
3 per band 21 (thus 20%) that can be directly overwritten at any
time. A read-modify-write may be required only when changing older
data, in this example, data written at the beginning of the first
filling stage.
[0090] The third filling stage and the fourth filling stage are not
depicted as drawings. In their approach they correspond to the
second filling stage as per FIG. 14. In each filling stage data are
added to the next inwardly adjacent tracks 3 in the bands 21. For
instance, in the third filling stage, data tracks 20 are written on
track pair (#002, #003) and track pair (#007, #008) in the 1st
band. No write amplification occurs when adding new data or when
changes are made to the last 20% of newly added data.
[0091] FIG. 15 shows the tracks 3 of a full disk surface 2 at the
end of the fifth and final filling stage. Data are added to the
tracks 3 adjacent to the guard tracks 14, for example track #004
and track #006 in the 1st band, for which the write element 16 may
be positioned on track pair (#004, #005) and track pair (#005,
#006), respectively. In the sixth embodiment, updates or changes to
the last 20% of newly or recently added data can be written
immediately, that is, without read-modify-write, even if the SMR
hard disk drive 1 is completely full.
[0092] When comparing the fifth and sixth embodiments, those
skilled in the art will recognize that the various strategies that
can be used to write data to the tracks 3 on the disk surfaces 2
have different advantages and/or disadvantages. Those skilled in
the art will therefore choose an embodiment or a variant that is
particularly suited to a specific purpose.
[0093] For instance, the fifth embodiment may not require any
read-modify-write operations up to a fill level of 60%, even in the
case of random write operations or when changing existing data.
Therefore, one conceivable application scenario would be a database
that increases in size slowly and has frequently changing
contents.
[0094] The sixth embodiment is characterized in that no
read-modify-write operations may be required to change any newly or
recently added data, even in the case of random write operations.
Therefore, one conceivable application scenario would be a file
server that stores large amounts of data, while the users typically
make changes to newly or recently added files, that is, files
pertaining to current topics or issues.
[0095] FIG. 16 through FIG. 18 show a seventh embodiment. The
effective track width of the write element 16 is three times as
wide as the track width 5 of the read element 17, as can be seen
from the read/write head 8 depicted in FIG. 16. The excess width 18
of the write element 16, as defined in the present disclosure, is
the difference between the effective track width of the write
element 16 and the track width 5 of the read element 17.
Accordingly, with regard to FIG. 16, the excess width 18 is the sum
of the length of the two arrows 18 on both sides of the read
element 17.
[0096] In this context, the term "excess width 18 of write element
16" is to be interpreted regardless of the position of the read
element 17 within the read/write head 8 and regardless of the
corresponding arrows 18 depicted in FIG. 16. E.g., the excess width
18 may be located on either sides of the write element 16,
depending on whether the write element 16 writes to a track 3 in
the upper or lower half of a band 21.
[0097] Since the write element 16 writes data tracks 20 of triple
track width 5, a guard region 14 that covers a width no less than
two tracks 3 is required (at least double track width 5). The
seventh embodiment utilizes symmetrical bands 21 that have a guard
region 14 in the middle of each band 21. Eight tracks 3 per band 21
may be used for storing data while two tracks 3 per band 21 are
required as guard region 14. As illustrated in FIG. 16 through FIG.
18, a disk surface 2 may contain 990 tracks, counted from track
#000 to track #989, grouped into 99 bands.
[0098] With regard to the order or sequence in which the tracks 3
on a disk surface 2 are written, the seventh embodiment makes use
of a strategy similar to that of the fifth embodiment, and may
therefore, inter alia, be suitable for files and/or databases whose
contents change frequently. For this purpose, filling an empty SMR
hard disk drive 1 may be considered as taking place in three phases
or filling stages.
[0099] FIG. 16 shows a disk surface 2 at the end of the first
filling stage, which may be reached at a fill level of 50%. Data
are added to four tracks 3 per band 21, for example track #000,
track #003, track #006, and track #009 in the 1st band, as
indicated by value "1" in the "Taken" column. The written data
tracks 20 do not overlap, with the exception of the guard regions
14. That is, the excess width 18 of the write element 16 is caught
by empty, adjacent tracks 3 or by the guard region 14. Hence, no
read-modify-write operations are required when updating existing
data.
[0100] FIG. 17 shows the second filling stage, which may correspond
to a fill level between 50% and 75%. Data are added to two tracks 3
per band 21, for example, track #002 and track #007 in the 1st band
by writing data tracks 20 on the triple sets of tracks (#002, #003,
#004) and (#005, #006, #007). Track #003 and track #006, which
already contain valid data, are overwritten, necessitating a
read-modify-write. Since this read-modify-write involves a single
track 3, practicable performance can be achieved up to a fill level
of 75%.
[0101] FIG. 18 shows the tracks 3 of a full disk surface 2 at the
end of the third and final filling stage. Data are added to the
last free tracks 3 in the bands 21, for example on track #001 and
track #008 in the 1st band. This results in increased write
amplification so that the last 25% of storage capacity may be
considered reserve capacity that runs with reduced performance.
[0102] Those skilled in the art will recognize that there is a wide
variety of ways and strategies in regard to the order or sequence
in which the tracks 3 on a disk surfaces 2 can be written. Various
embodiments may be combined and/or varied. Those skilled in the art
will therefore choose a suitable embodiment or variant.
[0103] Furthermore, a configuration option may be provided so that
users can select or change the strategy, order, or sequence in
which tracks 3 are written. This could be done as part of a
re-initialization that optimizes the SMR hard disk drive 1 for a
specific, or new, purpose. The hard disk controller 10 may also
change the strategy adaptively during operation, in order to
respond to the characteristics of the written data. E.g., the hard
disk controller 10 may determine the dominating task type, such as
adding new data to free disk space or changing existing data.
[0104] In some disclosed embodiments, when filling a hard disk
drive 1 with data, the read/write heads 8 switch to the next disk
surface 2 not until data have been added to each band 21, 22 of the
present disk surface 2. That is, data are written to a selection of
tracks 3 encompassing all bands 21, 22 on a disk surface 2, and
only then does a switch to the next disk surface 2 take place.
However, in other embodiments the read/write heads 8 may switch
between different disk surfaces 2 more frequently, for instance,
after each zone. Also, the read/write heads 8 may switch between
disk surfaces 2 in a different, or dynamic order. Examples may be
found in U.S. Pat. No. 8,699,185 B1, entitled "Disk drive defining
guard bands to support zone sequentiality when butterfly writing
shingled data tracks," the disclosure of which is hereby
incorporated by reference in its entirety.
[0105] In further embodiments the hard disk controller 10 may
optimize the position of stored data depending on weather the data
are changed frequently or seldom. Data that are changed frequently
may include, for instance, the file management table of a file
system, databases, or any other type of directory, table contents,
or index data that are often changed or updated during operation.
Rarely changed data may include any type of data that are stored
for archival purposes.
[0106] Frequently changed data may be stored on tracks 3 adjacent
to the guard regions 14 of the symmetrical bands 21, 22, whereas
data for archival purposes may be stored farther away from the
guard regions 14. In this way, frequently changed data can be
updated directly without read-modify-write. Updating archive data
may cause write amplification, though, due to the distance to the
guard regions 14.
[0107] For example, in the case of the first embodiment, as per
FIG. 4, frequently changing data may be written to tracks #104 and
#106, allowing an instant update without write amplification, and
data for archival purposes may be written, inter alia, to tracks
#101, #102, #108, and #109. In the case of the second embodiment,
as per FIG. 6, frequently changing data may be written to tracks
#101 and #108, adjacent to the guard regions 14, and archive data
may be stored, inter alia, on tracks #103 through #106.
[0108] In the case of the fifth and sixth embodiments, as per FIG.
12 and FIG. 15, frequently changing data may be located, for
instance, on tracks #004 and #006 in the 1st band and tracks #983
and #985 in the 90th band, allowing an instant update at any time
without read-modify-write. Depending on the required storage space,
archive data may be stored on the outer tracks 3 of the bands 21,
by way of example, tracks #000 and #010 in the 1st band and tracks
#979 and #989 in the 90th band.
[0109] Optionally, one or more disk surfaces 2 of the hard disk
drive 1 may be divided into areas with overlapping data tracks 20
and areas with conventional, non-overlapping tracks. The areas with
conventional, non-overlapping tracks may be used as fast write
caches. E.g., while the methods according to the present disclosure
may be applied to larger areas with overlapping data tracks 20,
conventional caching may be done in smaller areas with
non-overlapping tracks. More information about combining
overlapping and non-overlapping areas on a disk surface 2 may be
found in patent application US2014/0006707 A1, entitled "ICC-NCQ
Command Scheduling for Shingle-written Magnetic Recording (SMR)
Drives," the disclosure of which is hereby incorporated by
reference in its entirety.
[0110] As for the embodiments presented in this disclosure, the
read/write heads 8 used have write elements 16 twice or three times
as wide as their respective read elements 17. However, other
embodiments may have different width ratios. Generally speaking,
the track width of the write element 16 can be any value greater
than the track width 5 of the read element 17.
[0111] Furthermore, in some embodiments, the width of a guard
region 14 may be equal to the track width 5 or to multiples of the
track width 5. Thus, guard regions 14 may fit precisely into the
grid of tracks 3. However, in other embodiments, guard regions 14
with different widths may be implemented that are expressly not
multiples of the track width 5, but which, for example, are 1.5
times or 2.5 times the width of a track 3. It is to be explicitly
noted that the present disclosure is not limited to guard regions
14 consisting of one or two tracks 3. A guard region 14 may have
any suitable width. Also, the width of a guard region 14 may be
increased to enhance the reliability of stored data.
[0112] For illustrative purposes, and to keep the number of
depicted tracks 3 and/or physical sectors 4 manageable, all bands
15, 21, 22 or other sections of the disk surfaces 2 shown in the
drawings of the present disclosure comprise relatively few tracks 3
and/or physical sectors 4. It is to be expressly noted that actual
embodiments may have very large track counts and/or sector counts
and that all disclosed methods and devices can be implemented with
any number of tracks 3 and/or physical sectors 4.
[0113] Each disk surface 2 in the disk stack 13 need not
necessarily contain the same number of tracks 3, that is, each disk
surface 2 may have its own, individual track count. This shall also
apply to the bands 21, 22. Each individual band 21, 22 on a disk
surface 2 may comprise a different, e.g., optimized, number of
tracks 3.
[0114] The embodiments disclosed herein describe the invention
based on the example of an SMR hard disk drive 1. All embodiments
and further embodiments can, however, also be implemented by means
of other data carrier media, which work, by way of example, on
magnetic or optical bases. Also, recording data on a data carrier
media may be combined with or assisted by other known technologies,
such as "Heat-Assisted Magnetic Recording" (HAMR), "Two-Dimensional
Magnetic Recording" (TDMR), and/or "Bit Patterned Media" (BPM).
[0115] Although the description above contains many specificities,
these should not be construed as limiting the scope of the
embodiments but as merely providing illustrations of some of
several embodiments. Thus, the scope of the embodiments should be
determined by the appended claims and their legal equivalents,
rather than by the examples given.
* * * * *