US20150113239A1 - Creation and Management of Logical Volume Snapshots Under Hierarchical Storage System - Google Patents
Creation and Management of Logical Volume Snapshots Under Hierarchical Storage System Download PDFInfo
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- US20150113239A1 US20150113239A1 US14/516,815 US201414516815A US2015113239A1 US 20150113239 A1 US20150113239 A1 US 20150113239A1 US 201414516815 A US201414516815 A US 201414516815A US 2015113239 A1 US2015113239 A1 US 2015113239A1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F11/00—Error detection; Error correction; Monitoring
- G06F11/07—Responding to the occurrence of a fault, e.g. fault tolerance
- G06F11/14—Error detection or correction of the data by redundancy in operation
- G06F11/1402—Saving, restoring, recovering or retrying
- G06F11/1446—Point-in-time backing up or restoration of persistent data
- G06F11/1448—Management of the data involved in backup or backup restore
- G06F11/1451—Management of the data involved in backup or backup restore by selection of backup contents
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
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- G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
- G06F3/06—Digital input from, or digital output to, record carriers, e.g. RAID, emulated record carriers or networked record carriers
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- G06F3/0601—Interfaces specially adapted for storage systems
- G06F3/0602—Interfaces specially adapted for storage systems specifically adapted to achieve a particular effect
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- G06F3/0605—Improving or facilitating administration, e.g. storage management by facilitating the interaction with a user or administrator
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- G06F3/0602—Interfaces specially adapted for storage systems specifically adapted to achieve a particular effect
- G06F3/0614—Improving the reliability of storage systems
- G06F3/0619—Improving the reliability of storage systems in relation to data integrity, e.g. data losses, bit errors
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- G06F3/06—Digital input from, or digital output to, record carriers, e.g. RAID, emulated record carriers or networked record carriers
- G06F3/0601—Interfaces specially adapted for storage systems
- G06F3/0628—Interfaces specially adapted for storage systems making use of a particular technique
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- G06F2201/84—Using snapshots, i.e. a logical point-in-time copy of the data
Definitions
- the present invention relates to a storage system and, more specifically, to a method for creating and managing hierarchically managed logical volume snapshots in a storage system.
- data In storage systems, data (files) are hierarchically managed using relatively fast, higher-level storage such as a hard disk drive (HDD), and relatively slow, lower-level storage such as a tape drive.
- HDD hard disk drive
- LVM logic volume management
- logical volumes logically segmented into volume groups of more than one logical volume.
- time 0 In copy services providing various types of storage subsystems, file systems and applications in addition to this type of storage management, techniques are used to store images of data at a certain instant (hereinafter referred to as “Time 0”). Examples of these techniques include snapshots and flash copies. The detailed mechanisms of this technique differ depending on the hardware and software being used but pointer information at locations where files (data) are being stored at Time 0 is generally saved, and this pointer information is used to manage the original files and images created at Time 0. In the following explanation, the term “snapshot” is used synonymously with “flash copy”.
- snapshots are valid only for files stored on the disk at Time 0, and a snapshot cannot be created when the target file is not present on the disk.
- snapshots are of a disk on a single level, and can be created and managed by creating and using pointer data when valid data is present on the disk.
- a snapshot cannot be created if data is not present on the disk.
- Patent Literature 1 describes a file management method for hierarchical management of files using a disk and physical tape which includes snapshot files using i-nodes of each source file and i-nodes of each snapshot file for each source file. However, Patent Literature 1 does not describe a method for creating and managing snapshots when no valid data is present on the disk but valid data is present on physical tape.
- the present invention is a method for creating and managing snapshots of hierarchically managed logical volumes in a storage system.
- the storage system includes first level storage and second level storage lower than the first level storage. This method includes the steps of:
- the present invention is able to create and manage a snapshot of hierarchically managed logical volumes when the logical volume has migrated from the first level storage to the second level storage without directly having to immediately recall the logical volume from the second level storage to the first level storage.
- the method in one aspect of the present invention also includes the steps of:
- one aspect of the present invention is the ability to respond to the access request and properly manage the snapshot afterwards.
- the method in one aspect of the present invention also includes the step of:
- one aspect of the present invention is the ability to create and manage logical volumes and their snapshots stored in this location when the overwriting or deletion of a logical volume previously used in a command to create a snapshot is requested.
- the method in one aspect of the present invention also includes the step of:
- the method in one aspect of the present invention also includes the step of:
- FIG. 1 is a diagram showing a configuration example of a storage system used by the method of the present invention.
- FIG. 2 is a diagram showing an example of a data storage status.
- FIG. 3 is an image diagram showing a snapshot that was created in the situation shown in FIG. 2 .
- FIG. 4 is a flowchart of the method of the present invention.
- FIG. 5 is a diagram showing an example of a management table prepared in Step S 2 of FIG. 4 .
- FIG. 6 is a diagram showing the management table after an update.
- FIG. 7 is a diagram showing the management table after an update.
- FIG. 8 is a diagram showing the management table after an update.
- FIG. 9 is a diagram showing the management table after an update.
- FIG. 10 is a diagram showing the management table after an update.
- FIG. 11 is a diagram showing the management table after an update.
- FIG. 12 is a diagram showing the management table after an update.
- FIG. 1 is a diagram showing a configurational example of a storage system used by the method of the present invention.
- the storage system 10 includes first storage 101 and second storage 102 which can communicate so as to enable communication.
- FIG. 1 shows a configuration with the minimal requirements for hierarchical management.
- the storage system 10 can be connected to multiple hosts (servers), and can include multiple units of first storage 101 and second storage 102 .
- a configuration including the storage system 10 and the host 20 can serve as an entire system 1 (for example, a data system, or data management system) or as part of a system.
- the first storage 101 in the storage system 10 can be storage including a higher level disk (sometimes referred to as the disk cache or HDD below), and the second storage 102 can be storage including lower level physical tape (tape drive).
- the configuration (or combination) of first and second storage can be any hierarchically organized combination and is not restricted to combinations of disks and physical tape.
- the storage system is Virtual Tape Server TS7700® provided by the applicant, International Business Machines Corporation. (hereinafter referred to as the TS7700.)
- the TS7700 can include, as a minimal configuration, the disk cache and physical tape illustrated in the storage system 10 of FIG. 1 .
- FIG. 2 shows the storage states of data in the TS7700.
- the data written from the host 20 is written to the disk cache 101 in units known as “logical volumes” 30 .
- logical volumes 30 are segmented logically into volume groups composed of more than one physical volume.
- the host 20 issues a mount command for a logical volume 30 , and the logical volume 30 is read or written.
- the host 20 then rewinds, unloads, and ends access. After access has been ended, the data is moved from the disk cache 101 to physical tape 102 and hierarchically managed according to the policies established by the user for each logical volume 30 .
- data 40 inside the TS7700 is stored in one of the following three storage states.
- a transition from storage state A to storage state B is referred to as pre-migration
- a transition from storage state B to storage state C is referred to as migration
- transition from storage state C to storage state B is referred to as a recall.
- GPFS General Parallel File System®
- the GPFS provides a snapshot function on both the file system level and the individual file level.
- the logical volume which is the source of a snapshot is referred to as the original data and the image of the logical volume created at Time 0 is referred to as the snapshot.
- FIG. 3 shows an image when a snapshot has been created at Time 0 using a function provided by GPFS with regard to the storage states A, B and C shown in FIG. 2 .
- block 50 delineated by dotted lines is a snapshot of data 40 . Because data 40 is present in the disk cache 101 in storage states A and B, it can create a snapshot 50 properly at Time 0.
- FIG. 4 The following is an explanation with reference to FIG. 4 of the operational flow of the method of the present invention which is used to create and manage a snapshot of hierarchically managed logical volumes.
- the operational flow in FIG. 4 is embodied in the configuration shown in FIG. 1 by software executed by a computer (controller) in the storage system 10 .
- Step S 1 a command is received from the host to create a snapshot of the logical volumes. More specifically, the user issues a command to the storage system via the host or a management interface.
- Step S 2 a management table is prepared for managing the snapshot. More specifically, a DB2 table is prepared (duplicated) for the snapshot.
- a DB2 table refers to a DB2 table defined by the TS7700 as a relational database.
- the DB2 table includes various types of metadata used to manage the snapshot as explained below.
- FIG. 5 is an example of a management table (DB2 table) prepared in Step S 2 .
- LVOL_TOK, LVOL and LVOL_TO_PVOL in line 1 through line 3 include metadata information described below that is related to the original data (logical volumes), and LVOL_TOK_SNAP, LVOL_SNAP and LVOL_TO_PVOL_SNAP in line 4 through line 6 include metadata information described below that is related to the snapshot.
- LVOL_TOK This holds the status of each logical volume (whether or not the most recent data is present, etc.). An entry is created when the user defines a logical volume irrespective of whether the data is located on the disk or the physical tape.
- LVOL This holds information indicating in which physical volume the logical volume is located (whether or not the data is migrated or pre-migrated). As in the case of LVOL_TOK, an entry is created when the user defines a logical volume irrespective of whether the data is located on the disk or the physical tape.
- LVOL_TO_PVOL When each logical volume is migrated or pre-migrated, this holds information indicating whether or not the logical volume is located on physical tape. An entry is created when a logical volume has pre-migrated to physical tape.
- the management table is for logical volumes (original data) which have already migrated and are present only on physical tape.
- “migrated” is indicated for LVOL in line 2
- physical volume PVOLX is indicated as the storage location of the migrated logical volume (original data) for LVOL_TO_PVOL in line 3.
- LVOL_TOK in line 1 indicates that a snapshot (snap) does not have to be created of the initial state.
- LVOL_TOK_SNAP, LVOL_SNAP and LVOL_TO_PVOL_SNAP in line 4 through line 6 are not applicable (NA) in the initial state.
- Step S 3 the storage state of the logical volumes (original data) are detected in Step S 3 . More specifically, it is detected whether or not the logical volumes are in state A, B or C shown in FIG. 2 .
- Step S 4 it is determined whether or not the logical volumes (original data) has migrated. If the determination is YES, there is no data present on the disk cache. Therefore, an actual snapshot is not created and an image cannot be obtained at Time 0 even when a command has been issued to the GPFS to create a snapshot. Thus, the management table is updated in Step S 5 without performing the processing required to create a snapshot right away.
- FIG. 6 shows the management table after the update.
- “snap creation required” is recorded in LVOL_TOK and in LVOL_TOK_SNAP, which is the field indicating the current snapshot status. This indicates that another snapshot has to be created for each logical volume unit at a stage when the original data has been recalled.
- “migrated” is recorded in both LVOL_SNAP and LVOL which indicates that the logical volumes have migrated.
- the physical volume PVOLX of the migrated original data is recorded in LVOL_TO_PVOL_SNAP.
- Step S 4 When the determination in Step S 4 is NO, original data is present in the disk cache.
- Step S 5 a snapshot is created of the original data at Time 0, as shown in the examples of states A and B in FIG. 3 .
- the step goes to S 5 , and the management table is updated.
- FIG. 7 shows the updated management table after a snapshot has been created.
- “cached” refers to storage state A in FIG. 2 in which original data is present in the disk cache 101
- pre-migrated refers to storage state B in FIG. 2 in which original data is present in both the disk cache 101 and physical tape 102 .
- Time 0 snapshots of all the logical volumes managed by TS7700 have been completed at this point. However, an actual snapshot image is not created at Time 0 of the logical volumes which have migrated.
- a separate snapshot is created and managed for the migrated logical volumes.
- the “mmcrsnapshot” command in GPFS can be used to create a snapshot at once of all of the data in the managed file system.
- a snapshot of separate files can be created using the “mmclone” command.
- the TS7700 recalls migrated original data when the data has been accessed. When a snapshot is accessed, it is recalled from the physical tape written to LVOL_TO_PVOL_SNAP.
- (A2) Original data can be accessed from the host once it has been recalled and its snapshot is created in an instant.
- FIG. 8 shows the management table after it has been updated.
- LVOL_TOK and LVOL_TOK_SNAP have been changed from “snap creation required” to “snap created”, and LVOL and LVOL_SNAP have been changed to “pre-migrated”.
- LVOL_TOK has to be changed to “snap creation required”
- LVOL has to be updated to “cached” to indicate that data is present on the disk
- LVOL_TO_PVOL has to be deleted (NA).
- NA LVOL_TO_PVOL_SNAP
- LVOL_TOK, LVOL and LVOL_TO_PVOL are deleted and the management table is updated accordingly.
- the status of LVOL_TOK_SNAP, LVOL_SNAP and LVOL_TO_PVOL_SNAP are the same as case (B) above.
- FIG. 10 shows the management table after it has been updated.
- a snapshot does not have to be created if any of the following has occurred before a snapshot has been created using GPFS.
- the management table is updated in the following way without any recall because a snapshot does not have to be created of the original files.
- LVOL_TOK and LVOL_TOK_SNAP are changed from “snap creation required” to “snap creation not required”, LVOL_SNAP is updated to “cached” indicating that data is present on the disk, and LVOL_TO_PVOL_SNAP is deleted (NA).
- FIG. 11 shows the management table after it has been updated.
- the management table is updated in the following way.
- LVOL_TOK_SNAP, LVOL_SNAP and LVOL_TO_PVOL_SNAP are deleted (NA), and LVOL_TOK is changed from “snap creation required” to “snap creation not required”.
- FIG. 12 shows the management table after it has been updated.
- Embodiments of the present invention have been explained with reference to the drawings, but the present invention is not limited to these embodiments.
- hierarchical management was explained between a disk and physical tape.
- the present invention is not limited to this and can be applied to any system that is hierarchically managed using different levels.
- a similar mechanism can be realized by applying an existing snapshot function to an upper-level disk device and recording the state of data (metadata) which has been moved to a lower-level disk drive as metadata. Snapshot management can be performed using the same technique even when three or more levels are used.
Abstract
Description
- The present application is a continuation nonprovisional application claiming the priority of the filing date of the co-pending and commonly assigned U.S. patent application Ser. No. 14/488,548 (Attorney Docket No. JP920130087US1) entitled “Creation and Management of Logical Volume Snapshots Under Hierarchical Storage System,” filed on Sep. 17, 2014.
- The present invention relates to a storage system and, more specifically, to a method for creating and managing hierarchically managed logical volume snapshots in a storage system.
- In storage systems, data (files) are hierarchically managed using relatively fast, higher-level storage such as a hard disk drive (HDD), and relatively slow, lower-level storage such as a tape drive. In storage systems, logic volume management (LVM) is also performed using logical volumes logically segmented into volume groups of more than one logical volume.
- In copy services providing various types of storage subsystems, file systems and applications in addition to this type of storage management, techniques are used to store images of data at a certain instant (hereinafter referred to as “Time 0”). Examples of these techniques include snapshots and flash copies. The detailed mechanisms of this technique differ depending on the hardware and software being used but pointer information at locations where files (data) are being stored at Time 0 is generally saved, and this pointer information is used to manage the original files and images created at Time 0. In the following explanation, the term “snapshot” is used synonymously with “flash copy”.
- Existing snapshots are valid only for files stored on the disk at Time 0, and a snapshot cannot be created when the target file is not present on the disk. In other words, snapshots are of a disk on a single level, and can be created and managed by creating and using pointer data when valid data is present on the disk. A snapshot cannot be created if data is not present on the disk.
- However, when files are hierarchically managed using a disk and physical tape, valid data is sometimes present on the physical tape even when there is no valid data present on the disk. Also, data can be moved from disk to physical tape hierarchically. When files are hierarchically managed in these situations, it is difficult to create and manage snapshots by using the simple pointer information archived by the conventional snapshot functions.
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Patent Literature 1 describes a file management method for hierarchical management of files using a disk and physical tape which includes snapshot files using i-nodes of each source file and i-nodes of each snapshot file for each source file. However,Patent Literature 1 does not describe a method for creating and managing snapshots when no valid data is present on the disk but valid data is present on physical tape. - Therefore, it is an object of the present invention to provide a method for creating and managing snapshots of hierarchically managed logical volumes even in situations in which there is no valid data on a disk but there is valid data on a physical tape.
- The present invention is a method for creating and managing snapshots of hierarchically managed logical volumes in a storage system. The storage system includes first level storage and second level storage lower than the first level storage. This method includes the steps of:
- (a) receiving a command for creating a snapshot of the logical volume;
- (b) preparing a management table for managing the snapshot, the management table including first metadata indicating the creation status of the snapshot, second metadata indicating the management status of the snapshot, and third metadata indicating the storage location of the logical volume;
- (c) detecting the storage status of the logical volume; and
- (d) updating the management table without recalling the logical volume from the second level storage to the first level storage when the logical volume has migrated from the first level storage to the second level storage, the first metadata indicating that creation of a snapshot is required, the second metadata indicating that the logical volume has migrated, and the third metadata indicating that the second level storage is the storage location of the logical volume.
- By updating and reusing a management table to manage a snapshot, the present invention is able to create and manage a snapshot of hierarchically managed logical volumes when the logical volume has migrated from the first level storage to the second level storage without directly having to immediately recall the logical volume from the second level storage to the first level storage.
- The method in one aspect of the present invention also includes the steps of:
- (e) recalling the logical volume when access to the logical volume or the snapshot is requested;
- (f) creating a snapshot from the logical volume recalled to the first level storage; and
- (g) updating the management table, the first metadata indicating that the snapshot has been created, the second metadata indicating that the logical volume has pre-migrated, and the third metadata indicating that the second level storage is the storage location of the logical volume.
- By creating a snapshot and updating and reusing a management table when access to a logical volume or snapshot is requested, one aspect of the present invention is the ability to respond to the access request and properly manage the snapshot afterwards.
- The method in one aspect of the present invention also includes the step of:
- (h) updating the management table when overwriting of the logical volume or deletion of the logical volume is requested, the first metadata indicating that creation of a snapshot is not required, the second metadata indicating that the logical volume has migrated, and the third metadata indicating that the second level storage is the storage location of the logical volume.
- By not requiring the creation of a snapshot and keeping the second level storage as the storage location of logical volume, one aspect of the present invention is the ability to create and manage logical volumes and their snapshots stored in this location when the overwriting or deletion of a logical volume previously used in a command to create a snapshot is requested.
- The method in one aspect of the present invention also includes the step of:
- (i) updating the management table when overwriting of the snapshot is requested, the first metadata indicating that creation of a snapshot is not required, the second metadata indicating that the logical volume is located in the first level storage, and the third metadata indicating that deletion has been performed.
- The method in one aspect of the present invention also includes the step of:
- (j) updating the management table when deletion of the snapshot is requested, the first metadata indicating that deletion has been performed, the second metadata indicating that deletion has been performed, and the third metadata indicating that deletion has been performed.
-
FIG. 1 is a diagram showing a configuration example of a storage system used by the method of the present invention. -
FIG. 2 is a diagram showing an example of a data storage status. -
FIG. 3 is an image diagram showing a snapshot that was created in the situation shown inFIG. 2 . -
FIG. 4 is a flowchart of the method of the present invention. -
FIG. 5 is a diagram showing an example of a management table prepared in Step S2 ofFIG. 4 . -
FIG. 6 is a diagram showing the management table after an update. -
FIG. 7 is a diagram showing the management table after an update. -
FIG. 8 is a diagram showing the management table after an update. -
FIG. 9 is a diagram showing the management table after an update. -
FIG. 10 is a diagram showing the management table after an update. -
FIG. 11 is a diagram showing the management table after an update. -
FIG. 12 is a diagram showing the management table after an update. - The following is an explanation of an embodiment of the present invention with reference to the drawings.
FIG. 1 is a diagram showing a configurational example of a storage system used by the method of the present invention. Thestorage system 10 includesfirst storage 101 andsecond storage 102 which can communicate so as to enable communication.FIG. 1 shows a configuration with the minimal requirements for hierarchical management. Thestorage system 10 can be connected to multiple hosts (servers), and can include multiple units offirst storage 101 andsecond storage 102. A configuration including thestorage system 10 and thehost 20 can serve as an entire system 1 (for example, a data system, or data management system) or as part of a system. - In one embodiment, the
first storage 101 in thestorage system 10 can be storage including a higher level disk (sometimes referred to as the disk cache or HDD below), and thesecond storage 102 can be storage including lower level physical tape (tape drive). The configuration (or combination) of first and second storage can be any hierarchically organized combination and is not restricted to combinations of disks and physical tape. In the following explanation, the storage system is Virtual Tape Server TS7700® provided by the applicant, International Business Machines Corporation. (hereinafter referred to as the TS7700.) The TS7700 can include, as a minimal configuration, the disk cache and physical tape illustrated in thestorage system 10 ofFIG. 1 . -
FIG. 2 shows the storage states of data in the TS7700. The data written from thehost 20 is written to thedisk cache 101 in units known as “logical volumes” 30. As mentioned above,logical volumes 30 are segmented logically into volume groups composed of more than one physical volume. Thehost 20 issues a mount command for alogical volume 30, and thelogical volume 30 is read or written. Thehost 20 then rewinds, unloads, and ends access. After access has been ended, the data is moved from thedisk cache 101 tophysical tape 102 and hierarchically managed according to the policies established by the user for eachlogical volume 30. - As shown in
FIG. 2 ,data 40 inside the TS7700 is stored in one of the following three storage states. - A: Present only in the
disk cache 101 - B: Present both in the
disk cache 101 and onphysical tape 102 - C: Present only on
physical tape 102 - A transition from storage state A to storage state B is referred to as pre-migration, a transition from storage state B to storage state C is referred to as migration, and transition from storage state C to storage state B is referred to as a recall.
- In the TS7700, data in the disk cache is read and written via the General Parallel File System® (GPFS). The GPFS provides a snapshot function on both the file system level and the individual file level. In the following explanation, the logical volume which is the source of a snapshot is referred to as the original data and the image of the logical volume created at Time 0 is referred to as the snapshot.
-
FIG. 3 shows an image when a snapshot has been created at Time 0 using a function provided by GPFS with regard to the storage states A, B and C shown inFIG. 2 . InFIG. 3 , block 50 delineated by dotted lines is a snapshot ofdata 40. Becausedata 40 is present in thedisk cache 101 in storage states A and B, it can create asnapshot 50 properly at Time 0. - Because data is not present in the
disk cache 101 in storage state C, a snapshot cannot be created using GPFS even when there is valid (the latest)data 40 present on thephysical tape 102. Therefore, in order to create a snapshot of data in storage state C at Time 0, an operation has to be performed in advance to recall data on the physical tape and write the data to thedisk cache 101. - However, in the TS7700, a maximum of 2 million logical volumes can be defined. When there is a large amount of migrated logical volumes, it can take a long time to recall all of the logical volumes. Therefore, Time 0 itself cannot be defined. Also, all volumes cannot be recalled at once because of the limited disk cache capacity. Therefore, it is inappropriate and practically impossible to recall data on the physical tape in advance. This particular problem is to be solved by the method of the present invention explained in detail below.
- The following is an explanation with reference to
FIG. 4 of the operational flow of the method of the present invention which is used to create and manage a snapshot of hierarchically managed logical volumes. The operational flow inFIG. 4 is embodied in the configuration shown inFIG. 1 by software executed by a computer (controller) in thestorage system 10. - In Step S1, a command is received from the host to create a snapshot of the logical volumes. More specifically, the user issues a command to the storage system via the host or a management interface. In Step S2, a management table is prepared for managing the snapshot. More specifically, a DB2 table is prepared (duplicated) for the snapshot. Here, a DB2 table refers to a DB2 table defined by the TS7700 as a relational database. The DB2 table includes various types of metadata used to manage the snapshot as explained below.
-
FIG. 5 is an example of a management table (DB2 table) prepared in Step S2. In the management table, LVOL_TOK, LVOL and LVOL_TO_PVOL inline 1 throughline 3 include metadata information described below that is related to the original data (logical volumes), and LVOL_TOK_SNAP, LVOL_SNAP and LVOL_TO_PVOL_SNAP inline 4 throughline 6 include metadata information described below that is related to the snapshot. - (a) LVOL_TOK: This holds the status of each logical volume (whether or not the most recent data is present, etc.). An entry is created when the user defines a logical volume irrespective of whether the data is located on the disk or the physical tape.
- (b) LVOL: This holds information indicating in which physical volume the logical volume is located (whether or not the data is migrated or pre-migrated). As in the case of LVOL_TOK, an entry is created when the user defines a logical volume irrespective of whether the data is located on the disk or the physical tape.
- (c) LVOL_TO_PVOL: When each logical volume is migrated or pre-migrated, this holds information indicating whether or not the logical volume is located on physical tape. An entry is created when a logical volume has pre-migrated to physical tape.
- In the example shown in
FIG. 5 , the management table is for logical volumes (original data) which have already migrated and are present only on physical tape. As a result, “migrated” is indicated for LVOL in line 2, and physical volume PVOLX is indicated as the storage location of the migrated logical volume (original data) for LVOL_TO_PVOL inline 3. LVOL_TOK inline 1 indicates that a snapshot (snap) does not have to be created of the initial state. LVOL_TOK_SNAP, LVOL_SNAP and LVOL_TO_PVOL_SNAP inline 4 throughline 6 are not applicable (NA) in the initial state. - Returning to
FIG. 4 , the storage state of the logical volumes (original data) are detected in Step S3. More specifically, it is detected whether or not the logical volumes are in state A, B or C shown inFIG. 2 . In Step S4, it is determined whether or not the logical volumes (original data) has migrated. If the determination is YES, there is no data present on the disk cache. Therefore, an actual snapshot is not created and an image cannot be obtained at Time 0 even when a command has been issued to the GPFS to create a snapshot. Thus, the management table is updated in Step S5 without performing the processing required to create a snapshot right away. -
FIG. 6 shows the management table after the update. First, “snap creation required” is recorded in LVOL_TOK and in LVOL_TOK_SNAP, which is the field indicating the current snapshot status. This indicates that another snapshot has to be created for each logical volume unit at a stage when the original data has been recalled. Then, “migrated” is recorded in both LVOL_SNAP and LVOL which indicates that the logical volumes have migrated. The physical volume PVOLX of the migrated original data is recorded in LVOL_TO_PVOL_SNAP. - When the determination in Step S4 is NO, original data is present in the disk cache. In Step S5, a snapshot is created of the original data at Time 0, as shown in the examples of states A and B in
FIG. 3 . The step goes to S5, and the management table is updated.FIG. 7 shows the updated management table after a snapshot has been created. In the management table shown inFIG. 7 , “cached” refers to storage state A inFIG. 2 in which original data is present in thedisk cache 101, and “pre-migrated” refers to storage state B inFIG. 2 in which original data is present in both thedisk cache 101 andphysical tape 102. - Time 0 snapshots of all the logical volumes managed by TS7700 have been completed at this point. However, an actual snapshot image is not created at Time 0 of the logical volumes which have migrated. In the present invention, when any of the following events occurs after the Time 0 snapshot, a separate snapshot is created and managed for the migrated logical volumes. In one embodiment, the “mmcrsnapshot” command in GPFS can be used to create a snapshot at once of all of the data in the managed file system. A snapshot of separate files can be created using the “mmclone” command.
- (A) If Original Data or Snapshot has been Accessed (Logical Volumes are Read and Written)
- (A1) Because the host can only access files located in the disk cache, the TS7700 recalls migrated original data when the data has been accessed. When a snapshot is accessed, it is recalled from the physical tape written to LVOL_TO_PVOL_SNAP.
- (A2) Original data can be accessed from the host once it has been recalled and its snapshot is created in an instant.
- (A3) Afterwards, the management table is updated.
-
FIG. 8 shows the management table after it has been updated. - LVOL_TOK and LVOL_TOK_SNAP have been changed from “snap creation required” to “snap created”, and LVOL and LVOL_SNAP have been changed to “pre-migrated”.
- (B) If Original Files have been Overwritten
- When “Write From BOT (Beginning of Tape)” has occurred, the management table is updated in the following way. LVOL_TOK has to be changed to “snap creation required”, LVOL has to be updated to “cached” to indicate that data is present on the disk, and LVOL_TO_PVOL has to be deleted (NA). However, because an entry for the snapshot remains in LVOL_TO_PVOL_SNAP, the logical volumes of the original file present on the physical tape are not invalidated. In this case, there is no longer any need to create a snapshot, and future access is provided to the original file and snapshot as two separate files.
FIG. 9 shows the management table after it has been updated. - (C) If Original Files have been Deleted
- In this case, LVOL_TOK, LVOL and LVOL_TO_PVOL are deleted and the management table is updated accordingly. The status of LVOL_TOK_SNAP, LVOL_SNAP and LVOL_TO_PVOL_SNAP are the same as case (B) above.
FIG. 10 shows the management table after it has been updated. - A snapshot does not have to be created if any of the following has occurred before a snapshot has been created using GPFS.
- (D) If Snapshot Overwrite (Write from BOT) has Occurred
- In this case, the management table is updated in the following way without any recall because a snapshot does not have to be created of the original files. LVOL_TOK and LVOL_TOK_SNAP are changed from “snap creation required” to “snap creation not required”, LVOL_SNAP is updated to “cached” indicating that data is present on the disk, and LVOL_TO_PVOL_SNAP is deleted (NA).
FIG. 11 shows the management table after it has been updated. - (E) If Snapshot Deletion has Occurred
- In this case, the management table is updated in the following way. LVOL_TOK_SNAP, LVOL_SNAP and LVOL_TO_PVOL_SNAP are deleted (NA), and LVOL_TOK is changed from “snap creation required” to “snap creation not required”.
FIG. 12 shows the management table after it has been updated. - As mentioned above, three values can be applied to the fields indicating the “status of a current snapshot” added to LVOL_TOK and LVOL_TOK_SNAP: “snap creation not required”, “snap creation required”, and “snap created”. The logical volume and snapshot of “snap creation not required” are treated as separate logical volumes.
- Embodiments of the present invention have been explained with reference to the drawings, but the present invention is not limited to these embodiments. In the embodiments described above, hierarchical management was explained between a disk and physical tape. However, the present invention is not limited to this and can be applied to any system that is hierarchically managed using different levels. A similar mechanism can be realized by applying an existing snapshot function to an upper-level disk device and recording the state of data (metadata) which has been moved to a lower-level disk drive as metadata. Snapshot management can be performed using the same technique even when three or more levels are used.
-
- 1: Overall system
- 10: Storage system
- 20: Host, multiple hosts (servers)
- 30: Logical volume
- 40: Data
- 50: Snapshot
- 101: 1st storage medium (HDD, etc.)
- 102: 2nd storage medium (tape drive, etc.)
Claims (7)
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US9665436B2 (en) | 2017-05-30 |
US20150113238A1 (en) | 2015-04-23 |
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