Managing snapshot history in a data storage system

• US 20070067583A1
• Filed: 09/19/2005
• Published: 03/22/2007
• Est. Priority Date: 09/19/2005
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: XIV Ltd. (International Business Machines Corporation)
• Inventors: Zeidner, Efri, Zohar, Ofir, Schwartz, Shemer
• Granted Patent: US 7,836,266 B2
• Time in Patent Office: Days
• US Class Current: 711/162
• CPC Class Codes: G06F 11/1458 Management of the backup or restore process
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data

Abstract

A method for creating logical volume snapshots in a data storage system, including receiving a first write command to write first data to a partition of a logical volume, generating a first partition descriptor record (PDR), and storing the first data at a first physical location associated with the first PDR. A snapshot command is then received to form a snapshot of the logical volume, after which a second write command is received to write second data to the partition. In response to the second write command, a second PDR is generated and the second data is stored at a second physical location associated with the second PDR. A pointer between the first PDR and the second PDR is generated. In response to a read command indicating a number of a desired snapshot of the logical volume, the first PDR is accessed using the pointer.

Claims

1. A method for creating logical volume snapshots in a data storage system, comprising:

responsively to a first write command to write first data to a partition of a logical volume, generating a first partition descriptor record (PDR) and storing the first data at a first physical location associated with the first PDR;

subsequent to the first write command, receiving a snapshot command to form a snapshot of the logical volume;

subsequent to the snapshot command and responsively to a second write command to write second data to the partition of the logical volume, generating a second PDR and storing the second data at a second physical location associated with the second PDR, and generating a pointer between the first PDR and the second PDR; and

subsequent to the second write command and responsively to a read command indicating a number of a desired snapshot of the logical volume, accessing the first PDR using the pointer.

2. The method of claim 1, wherein receiving the snapshot command comprises receiving the command at a specific time and setting a global counter equal to the specific time.

3. The method of claim 1, wherein receiving the snapshot command comprises incrementing a global counter.

4. The method of claim 3, wherein generating the first PDR comprises generating a snapshot indicator of the first PDR.

5. The method of claim 4, wherein accessing the first PDR comprises comparing the snapshot indicator of the first PDR with the number of the desired snapshot.

6. The method of claim 1, wherein generating the first PDR comprises associating the partition of the logical volume with the first PDR.

7. The method of claim 6, wherein generating the second PDR comprises disassociating the partition from the first PDR and associating the partition with the second PDR.

8. The method of claim 6, wherein associating the partition with the first PDR comprises generating a further pointer to the first PDR in a partition hash table.

9. The method of claim 1 wherein generating the pointer between the first PDR and the second PDR comprises generating a binary tree of a series of PDRs.

10. The method of claim 9, wherein the binary tree is generated by an Adelson-Velskii and Landis (AVL) method.

11. The method of claim 1, wherein the logical volume comprises a source logical volume, wherein the partition comprises a first partition, the method comprising, responsively to a volume copy command to copy the source logical volume to a target logical volume:

generating a third PDR associated with the first physical location; and

associating the third PDR with the target logical volume.

12. Apparatus for creating snapshots in a data storage system, comprising:

a control unit which is adapted;

to generate a first partition descriptor record (PDR) responsively to a first write command to write first data to a partition of a logical volume,

to store the first data at a first physical location associated with the first PDR,

to receive a snapshot command to form a snapshot of the logical volume,

to generate a second PDR responsively to a second write command to write second data to the partition of the logical volume,

to store the second data at a second physical location associated with the second PDR,

to generate a pointer between the first PDR and the second PDR, and

to access the first PDR using the pointer, responsively to a read command indicating a number of a desired snapshot of the logical volume.

13. The apparatus of claim 12, wherein the control unit is adapted to receive the snapshot command at a specific time and to set a global counter equal to the specific time.

14. The apparatus of claim 12, wherein the control unit is adapted to increment a global counter.

15. The apparatus of claim 14, wherein the control unit is adapted to generate a snapshot indicator of the first PDR.

16. The apparatus of claim 15, wherein the control unit is adapted to compare the snapshot indicator of the first PDR with the number of the desired snapshot.

17. The apparatus of claim 12, wherein the control unit is adapted to associate the partition of the logical volume with the first PDR.

18. The apparatus of claim 17, wherein the control unit is adapted to disassociate the partition from the first PDR and to associate the partition with the second PDR.

19. The apparatus of claim 17, wherein the control unit is adapted to generate a further pointer to the first PDR in a partition hash table.

20. The apparatus of claim 12, wherein the control unit is adapted to generate a binary tree of a series of PDRs.

21. The apparatus of claim 20, wherein the control unit is adapted to generate the binary tree by an Adelson-Velskii and Landis (AVL) method.

22. The apparatus of claim 12, wherein the logical volume comprises a source logical volume, wherein the partition comprises a first partition, the control unit being further adapted, responsively to a volume copy command to copy the source logical volume to a target logical volume:

to generate a third PDR associated with the first physical location, and

to associate the third PDR with the target logical volume.