U.S. patent application number 11/492027 was filed with the patent office on 2006-11-16 for storage system, storage device, and remote copy method.
Invention is credited to Naohiro Fujii, Nobuyuki Saika.
Application Number | 20060259725 11/492027 |
Document ID | / |
Family ID | 35137856 |
Filed Date | 2006-11-16 |
United States Patent
Application |
20060259725 |
Kind Code |
A1 |
Saika; Nobuyuki ; et
al. |
November 16, 2006 |
Storage system, storage device, and remote copy method
Abstract
A first data transfer module sends update data to be written
into a primary volume to a second data transfer module; the second
data transfer module stores the update data into a secondary
volume, stores differential data written to a storage address for
the update data in the secondary volume into a second differential
volume, updates a second management information holding module, and
then informs completion of the data updating to the first data
transfer module; and the first data transfer module stores the
update data to an update address in the primary volume when the
information of completion of the data updating is received from the
second data transfer module, stores the differential data into a
first differential volume, and updates a first management
information holding module.
Inventors: |
Saika; Nobuyuki; (Yokosuka,
JP) ; Fujii; Naohiro; (Yokohama, JP) |
Correspondence
Address: |
MATTINGLY, STANGER, MALUR & BRUNDIDGE, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Family ID: |
35137856 |
Appl. No.: |
11/492027 |
Filed: |
July 25, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10898356 |
Jul 26, 2004 |
7103713 |
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11492027 |
Jul 25, 2006 |
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Current U.S.
Class: |
711/162 ;
711/165; 714/E11.12; 714/E11.126 |
Current CPC
Class: |
G06F 11/1456 20130101;
G06F 2201/84 20130101; G06F 11/1466 20130101 |
Class at
Publication: |
711/162 ;
711/165 |
International
Class: |
G06F 12/16 20060101
G06F012/16; G06F 13/28 20060101 G06F013/28 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2004 |
JP |
2004-103821 |
Claims
1. (canceled)
2. A storage system, comprising a primary disk subsystem having a
disk drive provided for normal operation, a secondary disk
subsystem having a disk drive that stores a duplicate of data
stored in the primary disk subsystem, and a communications line
that connects the primary disk subsystem and the secondary disk
subsystem, the primary disk subsystem comprising a primary volume
where normal reading and writing are performed, a first
differential volume that stores differential data of a snapshot of
the primary volume, a first management information holding module
that manages the differential data, and a first data transfer
module that transfers data to the secondary disk subsystem, the
secondary disk subsystem comprising a secondary volume that stores
a duplicate of the data stored in the primary volume, a second
differential volume that stores differential data of a snapshot of
the secondary volume, a second management information holding
module that manages the differential data, and a second data
transfer module that transfers data to the primary disk subsystem,
wherein: the first data transfer module sends update data to be
written into the primary volume to the second data transfer module;
the second data transfer module: stores the update data in the
secondary volume; stores the differential data stored at the update
address in the secondary volume, into the second differential
volume; updates the second management information holding module;
and then informs completion of data updating to the first data
transfer module; and the first data transfer module: when the
information of completion of the data updating is received from the
second data transfer module; stores the update data to the update
address in the primary volume; stores the differential data stored
at the update address in the primary volume, into the first
differential volume; and updates the first management information
holding module.
3.-6. (canceled)
7. The storage system according to claim 2, wherein: the first data
transfer module sends the update data to be written into the
primary volume, and the update address where the update data is to
be written, to the second data transfer module; and the second data
transfer module: reads the differential data stored in the update
address in the secondary volume and stores the differential data
into the second differential volume; stores the update data sent
from the first data transfer module to the update address in the
secondary volume; updates the second management information holding
module based on the storage address where the differential data is
to be stored into the second differential volume; and then informs
the completion of the data updating to the first data transfer
module.
8. A storage device used in a storage system comprising a primary
storage device having a disk drive provided for normal operation, a
secondary storage device having a disk drive that stores a
duplicate of data stored in the primary storage device, and a
communications line that connects the primary storage device and
the secondary storage device, the primary storage device comprising
a primary volume where normal reading and writing are performed, a
first differential volume that stores differential data of a
snapshot of the primary volume, a first management information
holding module that manages the differential data, and a first data
transfer module that transfers data to the secondary storage
device, the secondary storage device comprising a secondary volume
that stores a duplicate of the data stored in the primary volume, a
second differential volume that stores differential data of a
snapshot of the secondary volume, a second management information
holding module that manages the differential data, and a second
data transfer module that transfers data to the primary storage
device, wherein the first data transfer module: sends the update
data to be written into the primary volume to the second data
transfer module; stores the update data to the update address in
the primary volume when information of completion is received from
the second data transfer module; stores the differential data into
the first differential volume; and updates the first management
information holding module.
9.-11. (canceled)
12. A storage device used by a storage system comprising a primary
storage device having a disk drive provided for normal operation, a
secondary storage device having a disk drive that stores a
duplicate of data stored in the primary storage device, and a
communications line that connects the primary storage device and
the secondary storage device, the primary storage device comprising
a primary volume where normal reading and writing are performed, a
first differential volume that stores differential data of a
snapshot of the primary volume, a first management information
holding module that manages the differential data, and a first data
transfer module that transfers data to the secondary storage
device, the secondary storage device comprising a secondary volume
that stores a duplicate of the data stored in the primary volume, a
second differential volume that stores differential data of a
snapshot of the secondary volume, a second management information
holding module that manages the differential data, and a second
data transfer module that transfers data to the primary storage
device, wherein the second data transfer module: receives the
update data sent from the first data transfer module to be written
into the secondary volume; stores the update data into the
secondary volume; stores the differential data stored at the update
address in the secondary volume, into the second differential
volume; updates the second management information holding module;
and then informs completion of the data updating for updating data
to the primary storage device.
13.-16. (canceled)
17. The storage device according to claim 12, wherein the second
data transfer module: receives from the first data transfer module
the update data to be written into the primary volume and the
update address where the update data is to be written; reads the
differential data stored in the update address in the secondary
volume and stores the differential data into the second
differential volume; stores the received update data to the update
address in the secondary volume; updates the second management
information holding module based on the storage address where the
differential data is to be stored into the second differential
volume; and then informs the completion of the data updating to the
first data transfer module.
18. A remote copy method used in a storage system comprising a
primary disk subsystem having a disk drive provided for normal
operation, a secondary disk subsystem having a disk drive that
stores a duplicate of data stored in the primary disk subsystem,
and a communications line that connects the primary disk subsystem
and the secondary disk subsystem, the primary disk subsystem
comprising a primary volume where normal reading and writing are
performed, a first differential volume that stores differential
data of a snapshot of the primary volume, a first management
information holding module that manages the differential data, and
a first data transfer module that transfers data to the secondary
disk subsystem, the secondary disk subsystem comprising a secondary
volume that stores a duplicate of the data stored in the primary
volume, a second differential volume that stores differential data
of a snapshot of the secondary volume, a second management
information holding module that manages the differential data, and
a second data transfer module that transfers data to the primary
disk subsystem, the remote copy method comprising: a first step of
controlling the first data transfer module to send the update data
to be written into the primary volume to the second data transfer
module; a second step of controlling the second data transfer
module to: store the update data sent from the first data transfer
module into the secondary volume; store the differential data
written in the storage address where the update data is stored in
the secondary volume, into the second differential volume; update
the second management information holding module; and then inform
the completion of data updating to the first data transfer module;
and a third step of controlling the first data transfer module to:
store the update data to the update address in the primary volume
when a information of completion is received from the second data
transfer module; store the differential data into the first
differential volume; and update the first management information
holding module.
19.-20. (canceled)
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese
application P2004-103821 filed on Mar. 31, 2004, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND
[0002] This invention relates to a storage system having a snapshot
function, and more particularly to a technique for transferring
data of a snapshot.
[0003] In an information society, one important role of a storage
system that accumulates information is protecting data. The most
common method of protecting data is a backup that saves a duplicate
of data in a storage to a backup medium such as a tape. With the
backup, even when the data in the storage is lost due to failure, a
fault, an operational error, or the like, the data can be recovered
based on the backup, thereby enabling recovery of the data at the
time when saved and suppressing damage to a minimum.
[0004] However, as storage capacities expand, the amount of time
necessary to make backups becomes a problem. Moreover, in
applications that require frequent updating of data, even if the
backup is made once, difference vis-a-vis the backup expand
quickly. In the event of an accident, the damage may be great.
Thus, backups must be made more frequently. Furthermore, in order
to prepare for a case where a file is lost due to an operational
error, or a case where one wants to compare file contents with a
previous state, and other such cases, there is a desire to enable
regular backups to be referenced easily.
[0005] As a function of handling these types of applications, a
snapshot function has been receiving attention. The snapshot
function is a function which maintains a data image in the storage
currently being used at the moment when the snapshot is taken, and
also enables access by means other than the storage currently being
used. At the moment when the snapshot is obtained, the snapshot can
be used without waiting for completion of all the data in the
storage to be copied thus minimizing the backup time which was a
problem in making tape backups.
[0006] In order to maintain the snapshot, there is a method of
using a saving storage area to save the data at the time when the
snapshot is obtained (refer to U.S. Pat. No. 5,649,152).
[0007] According to this technique, once the snapshot of an
operating volume is obtained, each time when an update subsequently
occurs at a block that has not yet been updated, the old data in
that block is copied to the saving storage area, and a virtual
volume for providing the snapshot is also generated. When reading
from the virtual volume, if the block at the address to be read has
been copied to the saving storage area, that block is returned. If
there is no copy in the saving storage area, then no update has
occurred in the operating volume, so that the block at the same
address in the operating volume is returned.
[0008] According to this technique, as compared to the case of
saving in the separate volume all the data in the operating volume
at the time when the snapshot is obtained, the image of the volume
at the time when the snapshot is obtained can be maintained with
small storage capacities.
[0009] Furthermore, regarding migration of data stored in the
storage system, in order to migrate data being accessed from the
superior device (host), an extended data transfer function (XRC:
Extended Remote Copy) and a peer-to-peer data transfer function
(PPRC: Peer-to-peer Remote Copy) have been proposed by IBM, Inc.
(refer to "Implementing ESS Copy Services on S/390", IBM P.502.8.5
DASD migration).
SUMMARY
[0010] The above-mentioned snapshot is achieved by means of a
primary volume, a differential volume, and a mapping table.
However, when migrating snapshot data, no consideration was given
to synchronizing these three while copying. Therefore, for example,
when a time lag occurs in the copying between the primary volume,
the differential volume and the mapping table, the snapshot data is
not integrated during that period, and a problem occurred in that
the image (virtual volume) from the time when the snapshot was
created cannot be structured. Furthermore, even when the primary
volume and the differential volume have been copied, when a fault
occurs to the data transfer function and the mapping table is not
copied, there is a problem in that the virtual volume of the
snapshot cannot be composed.
[0011] It is therefore an object of this invention to provide a
storage system capable of safely copying snapshot data.
[0012] According to this invention, there is provided a storage
system, comprising a primary disk subsystem having a disk drive
provided for normal use, a secondary disk subsystem having a disk
drive that stores a duplicate of data stored in the primary disk
subsystem, and a communications line that connects the primary disk
subsystem and the secondary disk subsystem, the primary disk
subsystem including a primary volume where normal reading and
writing are performed, a first differential volume that stores
differential data of a snapshot of the primary volume, a first
management information holding module that manages the differential
data, and a first data transfer module that transfers data to the
secondary disk subsystem, the secondary disk subsystem including a
secondary volume that stores a duplicate of the data stored in the
primary volume, a second differential volume that stores
differential data of a snapshot of the secondary volume, a second
management information holding module that manages the differential
data, and a second data transfer module that transfers data to the
primary disk subsystem,
[0013] wherein:
[0014] the first data transfer module sends update data to be
written into the primary volume to the second data transfer
module;
[0015] the second data transfer module: stores the update data in
the secondary volume; stores the differential data written to the
update address in the secondary volume into the second differential
volume; updates the second management information holding module;
and then informs completion of data updating to the first data
transfer module; and
[0016] the first data transfer module: stores the update data to
the update address in the primary volume when the information of
completion of the data updating is received from the second data
transfer module; stores the differential data into the first
differential volume; and updates the first management information
holding module.
[0017] According to this invention, consistencies in the snapshot
data can be maintained, and disaster recovery can be enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a block diagram showing a construction of a
storage system according to a first embodiment of this
invention.
[0019] FIG. 2 is a block diagram showing a construction of a NAS
according to a first embodiment of this invention.
[0020] FIG. 3 is an explanatory diagram of management of a snapshot
according to a first embodiment of this invention.
[0021] FIG. 4 is another explanatory diagram of management of the
snapshot according to a first embodiment of this invention.
[0022] FIG. 5 is a flowchart of data transfer processing according
to a first embodiment of this invention.
[0023] FIG. 6 is a flowchart of data transfer processing according
to a second embodiment of this invention.
[0024] FIG. 7 is a flowchart of data transfer processing according
to a third embodiment of this invention.
[0025] FIG. 8 is a flowchart of local side data transfer
processing, which is part of data transfer processing according to
a fourth embodiment of this invention.
[0026] FIG. 9 is a flowchart of remote-side data receiving
processing 1, which is part of the data transfer processing
according to the fourth embodiment of this invention.
[0027] FIG. 10 is a flowchart of remote-side data receiving
processing 2, which is part of the data transfer processing
according to the fourth embodiment of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Hereinafter, explanation will be made of embodiments of this
invention, with reference to the drawings.
[0029] FIG. 1 is a block diagram showing a construction of a
storage system according to a first embodiment of this
invention.
[0030] A NAS (Network Attached Storage device) 1 is connected to a
disk subsystem 2. The local-side NAS 1 is connected via a network 6
to a client 7 using a CIFS (Common Internet File System), and to a
client 8 using an NFS (Network File System). The network 6, for
example, performs communications via TCP/IP or other such
protocols. It should be noted that, Fibre Channel or iSCSI
(internet SCSI) may also be used to perform the communications. The
NAS 1 is provided with a file server (NFS/CIFS server module), and
the file server provides file sharing service to the clients 7 and
8.
[0031] Furthermore, the NAS 1 is provided with a differential
snapshot module. The differential snapshot module uses a
differential snapshot creation program 122, a differential snapshot
management program 123 and a differential snapshot composition
program 124, which are described below, to create and maintain the
snapshot and compose the virtual volume.
[0032] The local-side disk subsystem 2 is provided with a plurality
of disk drives. The disk drives are set with logical units (LUs)
recognized by operating system as single unit of disks.
Furthermore, the disk drives constitute main volume groups, and the
main volume groups are provided with a primary volume 201, a
differential volume 202 and a mapping table 203.
[0033] Furthermore, the logical unit is constituted by a RAID
(Redundant Array of Independent Disks), thus giving redundancy to
the stored data. Therefore, even when a fault occurs to a part of
the disk drives, the stored data is not lost.
[0034] The primary volume 201 is a volume provided for normal
operation, which is accessed from the clients 7 and 8 to write data
therein and read data therefrom. The differential volume 202 stores
the data stored in the primary volume 201, when performing
copy-on-write of the snapshot. The mapping table 203 stores
relationships between the primary volume 201 and the differential
volume 202, for each snapshot generation.
[0035] Furthermore, the disk subsystem 2 is provided with a remote
copy module. The remote copy module detects addresses where changes
occurred in the data stored in the main volume group, and transfers
data to a remote-side disk subsystem 4, and is realized by
executing a remote copy program 404 stored in the main volume
group.
[0036] The remote side is provided with a remote-side NAS 3 and the
remote-side disk subsystem 4, and can provide the same functions as
the local-side NAS 1 and the local-side disk subsystem 2.
[0037] The local side and the remote side are connected through a
data transfer network 5. The network 5 is connected so as to enable
transfer of data between the local-side NAS 1 and the remote-side
NAS 3, and between the local-side disk subsystem 2 and the
remote-side disk subsystem 4, to send and receive signals (data and
control signals) via a TCP/IP protocol.
[0038] It should be noted that, the network 5 may also be a SAN
(Storage Area Network), where signals (data and control signals)
are sent and received via a Fibre Channel protocol that is
appropriate for data transfer.
[0039] It should be noted that, data backup from the local side to
the remote side, can be performed between the NASs 1 and 3, or
between the disk subsystems 2 and 4. In the following embodiments,
explanations will be given regarding data backups between the disk
subsystems 2 and 4, but this invention may also be applied in data
backups between the NASs 1 and 3.
[0040] Furthermore, the explanation has been given regarding the
embodiment where the NAS and the disk subsystem are provided
separately on both the local side and the remote side, but this
invention may be applied in a storage system where the NAS and the
disk subsystem are integrated into a single unit.
[0041] FIG. 2 is a block diagram showing a construction of the NAS
1 according to a first embodiment of this invention.
[0042] The NAS 1 is provided with a CPU 11, a memory 12, a network
interface 14, and a storage interface 15.
[0043] The network interface 14 sends and receives data and control
signals to/from the clients 7 and 8 via a TCP/IP protocol.
[0044] The storage interface 15 sends and receives data and control
signals to/from the disk subsystem 2, using the Fibre Channel.
[0045] The memory 12 is provided with a cache memory for
temporarily storing data that is read and written to/from the disk.
Furthermore, the memory 12 stores a file server program 121, the
differential snapshot creation program 122, the differential
snapshot management program 123, the differential snapshot
composition program 124, and a file system program 125. The CPU 11
calls up and executes those programs, whereby various processings
are performed.
[0046] The file server program 121, responding to a data access
request from the clients 7 and 8, requests the file system program
125 to execute read processing from files or directories or write
processing to files or directorys, and sends the result of this
execution back to the clients 7 and 8.
[0047] The snapshot creation program 122 receives a snapshot
creation request, and then creates the snapshot of the disk
subsystem 2 primary volume. Specifically, the mapping table 203
area is set.
[0048] The differential snapshot management program 123 manages the
differential volume 202 storing the differential data necessary to
maintain the snapshot, and performs processing to write data
according to the request from the file system program 125 and to
maintain the snapshot. Specifically, when using the mapping table
203 to write the data to the primary volume 201, the differential
data stored in the primary volume 201 is copied to the differential
volume, and after that the update data is written into the primary
volume 201 to update the stored content.
[0049] The differential snapshot composition program 124 uses the
primary volume 201 and the differential volume 202 to read virtual
volume according to the request from the file system program 125
(i.e., processing to make the snapshot usable). Specifically, the
mapping table 203 is referenced, it is determined whether to read
data from the primary volume 201 or from the differential volume
202, the data is then read from the determined volume, and then a
virtual volume for providing the data stored in the primary volume
201 at the time of receiving the snapshot creation request is then
composed.
[0050] The file system program 125, in response to read request to
the files or directories and write request from the files or
directories issued by the file server program 121 or the
differential snapshot management program 123, designates the volume
where a file and directory are being stored, and a block address
and size to be accessed. Furthermore, requests for virtual volume
read processing and write processing are issued to the snapshot
composition program 124.
[0051] Next, explanation will be given regarding management of the
snapshot. FIGS. 3 and 4 are explanatory diagrams of snapshot
management according to a first embodiment of this invention.
[0052] The snapshot creation program 122 receives the snapshot
creation request, and then registers identification information for
the new virtual volume (in the "snapshot 1 differential volume
storage address" column of mapping table in FIG. 3) into the
mapping table 203. This virtual volume block, at the point in time
when the snapshot is created, is associated in a one-to-one
correspondence with a block in the primary volume 201, since no
data storage address is registered in the differential volume
storage address column in the mapping table 203.
[0053] After that, when updating the data inside the primary volume
201, the snapshot management program 123 copies the pre-update
differential data in the primary volume 201 into the differential
volume 202, and after copying, writes the update data into the
primary volume 201, thus updating the primary volume 201 storage
content. It should be noted that, the copying of the data from the
primary volume 201 to the differential volume 202 may be performed
by actually moving the data, or by rewriting a pointer that
indicates the address where the data is stored.
[0054] Furthermore, the snapshot management program 123 updates the
mapping table 203, so as to establish a correspondence between the
block in the virtual volume 202 corresponding to the block in the
primary volume 201 where the data was updated, and the block in the
differential volume 202 storing the data (i.e., the pre-update
data) that had been stored in the primary volume 201 at the time
when the snapshot was created.
[0055] For example, in FIG. 4, between the creation of the snapshot
1 and the creation of a snapshot 2, when rewriting the data stored
in P1 of the primary volume to "aaaaa", differential data "AAAAA"
that was stored in P1 of the primary volume is copied into D1 of
the differential volume, and then the update data "aaaaa" is stored
in P1 of the primary volume. At this time, the differential data's
storage address D1 is stored in the P1 column of the mapping table.
Furthermore, a "1" indicating that differential data has been
stored for the snapshot 1 is stored as the most significant bit of
changed/unchanged bit map in the mapping table.
[0056] Furthermore, from the creation of the snapshot 2 until the
present, when rewriting P2 in the primary volume to "bbbbb",
differential data "BBBBB" that was stored in P2 of the primary
volume is copied into D2 of the differential volume, and then the
update data "bbbbb" is stored into P2 of the primary volume. At
this time, the differential data's storage address D2 is stored in
the P2 column of the mapping table. At this time, D2 is stored not
only in the storage address of the differential volume of the
snapshot 2, but also in the storage address of the differential
volume of the snapshot 1 which requires this differential data.
Furthermore, a "1" indicating that differential data is stored for
the snapshots 1 and 2 is stored in the most significant bit and the
second significant of the changed/unchanged bit map in the mapping
table (i.e., "11" is stored in the bitmap showing whether there is
a change).
[0057] When the file system program 125 issues a virtual volume
access request to the snapshot composition program 124, the
snapshot composition program 124 references to the mapping table,
and reads out data from the primary volume block or the
differential volume block that is associated with the virtual
volume block. Therefore, the file system program 125 accesses the
virtual volume, so as to be able to use the information stored in
the primary volume at the time when the snapshot creation request
was issued. Therefore, a snapshot image in the file system can be
provided to the clients 7 and 8.
[0058] In other words, the virtual volume is a virtual volume that
is constituted of storage area inside one or a plurality of disk
devices. Actually, the virtual volume is constituted of a subset of
the blocks in the primary volume, and a subset of the blocks in the
differential volume.
[0059] For example, in FIG. 4, the virtual volume corresponding to
the primary volume at the time when the snapshot 1 is created is
obtained by reading out and composing the following: "AAAAA" which
is the differential data corresponding to P1 and is stored in D1 in
the differential volume, "BBBBB" which is the differential data
corresponding to P2 and is stored in D2 of the differential volume,
and "CCCCC" which is stored in P3 in the primary volume (since
there is no differential data corresponding to P3, the data is read
out from the primary volume).
[0060] FIG. 5 is a flowchart of data transfer processing according
to a first embodiment of this invention.
[0061] First, when the data update request from the differential
snapshot management program 123 is received (i.e., the occurrence
of copy-on-write based on the update request) (S101), a local-side
data transfer module analyzes the update request and extracts the
update data (the data to be written to the disk) and the data
update address (the address where the data is to be written), which
are included in the update request (S102). After that, the
differential data (prior-to-update data) stored at the update
address in the primary volume 201 is read out (S103). Furthermore,
the area in the differential volume for storing the differential
data is determined, and mapping information after data is updated
(information about the area storing the differential data that is
written to the update address in the mapping table) is created
(S104). It should be noted that, at this stage, the mapping
information is not written into the mapping table 203.
[0062] Then, the data which has been obtained as described above,
the update address, the differential data, and the mapping
information are combined as a group and included in a request, and
this request is sent to the remote-side disk subsystem 4
(S105).
[0063] The remote-side data transfer module monitors the receiving
of the request (S106). When the remote-side data transfer module
receives the request from the local-side disk subsystem 2, the
update data, the update address, the differential data, and the
mapping information are extracted from the request that was
received (S107 to S110).
[0064] Then, the update data extracted from the request is written
to the update address in a primary volume 401 (S111), and the
differential data extracted from the request is written into the
differential volume 402 (S112). The address where this differential
data is written is the storage area of the differential data
included in the mapping information that was extracted from the
request. Then, the mapping information extracted from the request
is written to the mapping table 403 (S113). After that, the
updating of the data on the remote side is complete, so a
completion is informed to the local-side disk subsystem 2
(S114).
[0065] The local-side data transfer module that sent the request
monitors the receiving of the information of completion (S115).
Then, when the local-side data transfer module receives the
information of completion from the remote-side disk subsystem 4,
the update data is written into the primary volume 201 (S116), and
then the differential data that was read at S103 is written into
the differential volume 202 (S117), and the mapping information
created at S104 is written into the mapping table (S118).
[0066] In this way, in the data transfer processing according to
the first embodiment, the update data necessary for the
differential snapshot, the differential data, and the mapping
information are combined as a group, and are sent from the
local-side disk subsystem 2 to the remote-side disk subsystem 4.
Therefore, even if damage occurs while the data is transferred from
the local side to the remote side, inconsistencies in the snapshot
data can be avoided.
[0067] FIG. 6 is a flowchart of data transfer processing according
to a second embodiment of this invention. In the data transfer
processing according to the second embodiment, the data transferred
from the local side to the remote side is kept at a minimum level,
and the transfer performance precedes.
[0068] First, when the data update request by the differential
snapshot management program 123 (i.e., the occurrence of the
copy-on-write based on the update request) is received (S121), the
local-side data transfer module analyzes the update request, and
extracts the update data (the data to be written to the disk) and
the data update address (the address where the data is to be
written), which are included in the update request (S122). Then,
the update data and the update address which were obtained are
included in the request, and this request is sent to the
remote-side disk subsystem 4 (S123).
[0069] The remote-side data transfer module monitors the receiving
of the request (S124). When the remote-side data transfer module
receives the request from the local-side disk subsystem 2, the
update data and the update address are extracted from the received
request (S125 and S126).
[0070] Then, the differential data that is stored in the update
address in the primary volume 401 (the update address extracted
from the request) is read out (S127). Then, the area for writing
the differential data is secured in the differential volume 402
(S128), and the differential data that was read out at S127 is
written into the area in the differential volume 402 which was
secured at S128 (S129). After that, the update data that was
extracted from the request is written to the update address
extracted from the request (S130), and the area where the
differential data was stored is written to the update address of
the mapping table (S131). After that, since the updating of the
data on the remote side is complete, the completion is informed to
the local-side disk subsystem 2 (S132).
[0071] The local-side data transfer module that sent the request
monitors the receiving of the information of completion (S133).
Then, when the local-side data transfer module receives the
information of completion from the remote-side disk subsystem 4,
the differential data that is stored in the update address in the
primary volume 201 is read out and the update data is written to
the update address (S134). Then, the differential data read from
the update address is stored into the differential volume 202
(S135), and the area where the differential data is stored is
written to the update address of the mapping table (S136).
[0072] In this way, in the data transfer processing according to
the second embodiment, the data that is transferred from the local
side to the remote side is limited to only the update data and the
storage address, and the other information that is necessary for
the copy-on-write (i.e., the differential data and the mapping
table information) is obtained on the remote side. Accordingly, the
data that is transferred from the local side to the remote side can
be kept at the minimum level, the time necessary for the transfer
processing can be shortened, and the transfer performance can be
improved. Furthermore, increases in the load on the data transfer
network 5 can be reduced.
[0073] FIG. 7 is a flowchart of data transfer processing according
to a third embodiment of this invention. In the data transfer
processing according to the third embodiment, after confirming that
the differential data and the mapping table match each other, the
data is then updated, thus making the data synchronization more
reliable.
[0074] First, when the data update request by the differential
snapshot management program 123 (i.e., the occurrence of the
copy-on-write based on the update request) is received (S141), the
local-side data transfer module analyzes the update request, and
extracts the update data (the data to be written to the disk) and
the data update address (the address where the data is to be
written), which are included in the update request (S142). Then,
the differential data (the pre-update data) stored in the update
address in the primary volume 201 is read out (S143). Furthermore,
the area in the differential volume to store the differential data
is determined, and the mapping information after data is updated
(the information about the area for storing the differential data,
which is written in the update address of the mapping table) is
created (S104). It should be noted that at this stage, the mapping
information is not written into the mapping table 203.
[0075] Then, the obtained update data, the update address, the
differential data, and the mapping information are combined as a
group and included in a request, and this request is sent to the
remote-side disk subsystem 4 (S145).
[0076] The remote-side data transfer module monitors the receiving
of the request (S146). When the remote-side data transfer module
receives the request from the local-side disk subsystem 2, the
update data, the update address, the differential data, and the
mapping information are extracted from the request that was
received (S147 through S150).
[0077] Then, it is determined whether the data that is stored in
the update address of the primary volume 401 is equivalent to the
differential data that was extracted from the request (S151). For
the negative result, it is then determined that the transferred
data is irregular, and an error is informed to an administrator
(S162). On the other hand, for the positive result, it is
determined that the transferred data is not irregular, so that the
update data that was extracted from the request is written to the
update address in the primary volume 401 (S152).
[0078] Then, the differential data that was extracted from the
request is written into the differential volume 402 (S153). The
address where the differential data is written corresponds to the
storage area of the differential data that is included in the
mapping information extracted from the request. After that, the
mapping information after data is updated (the information about
the area for storing the differential data written to the update
address in the mapping table) is created (S154).
[0079] Then, it is determined whether the mapping information
created at S154, and the mapping information extracted from the
request, match each other (S155). When the result is that both sets
of mapping information do not match each other, it is then
determined that the transferred data is irregular, and an error is
informed to the administrator (S162). It should be noted that at
this time the differential data is written to the update address of
the primary volume 401, or the data that was written into the
differential volume 402 is deleted, whereby the primary volume 401
and the differential volume 402 may return to the pre-update
state.
[0080] On the other hand, if both sets of mapping information match
each other, then it is determined that the transferred data does
not have fault, and the mapping information extracted from the
request is written into the mapping table 403 (S156). After that,
since the updating of the data on the remote side is complete, a
completion is informed to the local-side disk subsystem 2
(S157).
[0081] The local-side data transfer module that sent the request
monitors the receiving of the information of completion (S158).
Then, when the local-side data transfer module receives the
information of completion from the remote-side disk subsystem 4,
the update data is written into the primary volume 201 (S159), the
differential data that was read at S143 is written into the
differential volume 202 (S160), and the mapping information created
at S144 is written into the mapping table (S161).
[0082] In this way, in the data transfer processing according to
the third embodiment, the update data, the storage address of the
update data, the differential data, and the mapping information are
transferred from the local side to the remote side, and it is
confirmed that the differential data on the local side and the
differential data on the remote side match each other before
writing the update data. Furthermore, it is confirmed that the
mapping information created on the local side and the mapping
information created on the remote side match each other before
updating the mapping table. Therefore, in addition to the effects
of the first embodiment, the reliability of the data transfer can
be improved even further.
[0083] FIGS. 8 to 10 are flowcharts of data transfer processing
according to a fourth embodiment of this invention. The data
transfer processing of the fourth embodiment differs from the
processing in the embodiments mentioned above in that a data
transfer method changes depending on the level of congestion on the
data transfer network 5.
[0084] FIG. 8 is a flowchart of data transfer processing of the
local-side disk subsystem.
[0085] First, when the data update request by the differential
snapshot management program 123 (i.e., the occurrence of the
copy-on-write based on the update request) is detected (S171), the
local-side data transfer module analyzes the update request, and
extracts the update data (the data to be written to the disk) and
the data update address (the address where the data is to be
written), which are included in the update request (S172). Then,
the differential data (the pre-update data) stored, in the update
address in the primary volume 201 is read out (S173). Furthermore,
the area in the differential volume for storing the differential
data is determined, and the mapping information after data is
updated (the information about the area for storing the
differential data, which is written in the update address of the
mapping table) is created (S174). It should be noted that at this
stage, the mapping information is not written into the mapping
table 203.
[0086] After that, the local-side data transfer module monitors the
usage rate of the data transfer network 5 and calculates this usage
rate (S175). This usage rate can be calculated, for example, by
dividing the amount of data sent for the past 1 hour by the line
speed per hour (the amount of data that can be transferred per
hour).
[0087] Then, the calculated usage rate and a pre-set maximum value
are compared (S176). When the result is that the network usage rate
exceeds the maximum value, it is then determined that the load on
the data transfer network 5 is great. Then, the obtained update
data and update address are included in a request, and the request
is sent to the receiving processing 1 of the remote-side disk
subsystem 4 (S177).
[0088] On the other hand, if the network usage rate is not beyond
the maximum value, then it is determined that the load on the data
transfer network 5 is small (or there is still room), so that the
obtained update data, update address, differential data and mapping
information are combined as a group and included in the request,
and the request is sent to the receiving processing 2 of the
remote-side disk subsystem 4 (S178).
[0089] The local-side data transfer module that sent the request
monitors the receiving of the information of completion (S179).
Then, when the local-side data transfer module receives the
information of completion from the remote-side disk subsystem 4,
the update data is written into the primary volume 201 (S180), and
the differential data that was read out at S173 is written into the
differential volume 202 (S181), and the mapping information that
was created at S174 is written into the mapping table (S182).
[0090] FIG. 9 is a flowchart of the receiving processing 1 by the
remote-side disk subsystem.
[0091] The remote-side data transfer module monitors the receiving
of the request (S191). When the remote-side data transfer module
receives the request for the receiving processing 1 from the
local-side disk subsystem 2, the update data and the update address
are extracted from the received request (S192 and S193).
[0092] Then, the differential data being stored in the update
address in the primary volume 401 (the update address extracted
from the request) is read out (S194). Then, area for writing the
differential data is secured in the differential volume 402 (S195),
and the differential data that was read out at S194 is written into
the area of the differential volume 402 that was secured at S195
(S196). After that, the update data that was extracted from the
request is written to the update address that was extracted from
the request (S197). The area where the differential data is stored
is written to the update address in the mapping table (S198). After
that, since the updating of the data on the remote side is
complete, a completion is informed to the local-side disk subsystem
2 (S199).
[0093] FIG. 10 is a flowchart of the receiving processing 2 by the
remote-side disk subsystem.
[0094] The remote-side data transfer module monitors the receiving
of the request (S201). When the remote-side data transfer module
receives the request for the receiving processing 1 from the
local-side disk subsystem 2, the update data, the update address,
the differential data, and the mapping information are extracted
from the request that was received (S202 to S205).
[0095] Then, it is determined whether the data that is stored in
the update address of the primary volume 401 is equivalent to the
differential data that was extracted from the request (S206). For
the negative result, it is then determined that the transferred
data is irregular, and an error is informed to an administrator
(S213). On the other hand, for the positive result, then it is
determined that the transferred data is not irregular, so that the
update data that was extracted from the request is written to the
update address in the primary volume 401 (S207).
[0096] Then, the differential data that was extracted from the
request is written into the differential volume 402 (S208). The
address where the differential data is written corresponds to the
storage area of the differential data that is included in the
mapping information extracted from the request. After that, the
mapping information after data is updated (the information about
the area for storing the differential data written to the update
address in the mapping table) is created (S209).
[0097] Then, it is determined whether the mapping information
created at S209, and the mapping information extracted from the
request, match each other (S210). When the result is that both sets
of mapping information do not match each other, it is then
determined that the transferred data is irregular, and an error is
informed to the administrator (S213). It should be noted that at
this time the differential data is written to the update address of
the primary volume 401, or the data that was written into the
differential volume 402 is deleted, whereby the primary volume 401
and the differential volume 402 may return to the pre-update
state.
[0098] On the other hand, if both sets of mapping information match
each other, then it is determined that the transferred data is not
irregular, and the mapping information extracted from the request
is written into the mapping table 403 (S211). After that, since the
updating of the data on the remote side is complete, a completion
is informed to the local-side disk subsystem 2 (S212).
[0099] In this way, in the data transfer processing according to
the fourth embodiment, depending on the load status (line usage
rate) of the data transfer network 5 connected to the local side
and the remote side, the data transferred from the local side to
the remote side changes. That is, when the lines are congested, the
volume of transferred data is reduced, and when the lines are not
congested, redundant data is added for the copy-on-write, thus
securing reliability.
[0100] While the present invention has been described in detail and
pictorially in the accompanying drawings, the present invention is
not limited to such detail but covers various obvious modifications
and equivalent arrangements, which fall within the purview of the
appended claims.
* * * * *