Cloning technique for efficiently creating a copy of a volume in a storage system

• US 20050246397A1
• Filed: 04/30/2004
• Published: 11/03/2005
• Est. Priority Date: 04/30/2004
• Status: Active Grant

• Current Assignee: NetApp, Inc.
• Original Assignee: NetApp, Inc.
• Inventors: Fair, Robert L., Edwards, John K.
• Granted Patent: US 7,409,511 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/10 File systems; File servers

Abstract

A cloning technique enables efficient and substantially instantaneous creation of a clone that is a writable copy of a “parent” virtual volume (vvol) in an aggregate of a storage system. A base snapshot is provided from the parent vvol. In addition, a new vvol is created, along with a new file system identifier, a new subdirectory in the aggregate and a new storage label file. The new vvol is embodied as a clone and comprises an appropriately sized container file, wherein initially the container file has no data. Moreover, a volume information (volinfo) block for the clone is created that is a slightly modified version of the volinfo block from the base snapshot; the modified volinfo block is written to the container file. The clone is then instantiated by loading a file system associated with the new vvol onto the clone and bringing the clone “online”.

Claims

1. A method for efficiently creating a copy of a parent virtual volume (vvol) in an aggregate of a storage system, the method comprising the steps of:

providing a base snapshot of the parent vvol;

creating a new vvol embodied as a clone, the clone comprising a container file;

modifying a volume information (volinfo) block for the clone, the modified volinfo block comprising a modified version of a volinfo block from the base snapshot;

writing the modified volinfo block to the container file; and

instantiating the clone to service storage requests directed to the storage system.

2. The method of claim 1 wherein the step of providing comprises one of the steps of:

generating a snapshot within the parent vvol; and

choosing an existing snapshot from the parent vvol.

3. The method of claim 1 wherein the step of creating comprises the step of creating a new file system identifier (fsid) subdirectory in the aggregate and a new storage label file.

4. The method of claim 1 wherein the step of instantiating comprises the steps of:

loading a file system associated with the new vvol onto the clone; and

bringing the clone online, with the clone owning only the modified volinfo block.

5. The method of claim 1 wherein the modified volinfo block forms a root of a modified volinfo block buffer tree that is similar to a parent volinfo block buffer tree of the parent vvol and wherein the step of writing comprises the step of accessing all blocks of the parent volinfo block buffer tree when traversing the modified volinfo block buffer tree.

6. A system adapted to efficiently creating a copy of a parent virtual volume (vvol) in an aggregate of a storage system, the system comprising:

disks coupled to the storage system and configured to store information served by the storage system;

a file system executing on the parent vvol of the storage system, the file system logically organizing the information as a structure of files and blocks on the disks;

a base snapshot sharing a parent container file represented as a parent buffer tree having a plurality of blocks in the aggregate, the plurality of blocks including level 0 data blocks that comprise all blocks used by the parent vvol, wherein one of the level 0 blocks is a snapshot volinfo block, the base snapshot sharing data structures with the file system executing on the parent vvol; and

a clone comprising a clone container file represented as a clone buffer tree having a plurality of blocks in the aggregate, the plurality of blocks including level 0 data blocks comprising all blocks used by the clone, wherein the clone container file initially contains only a modified volinfo block stored in one of the level 0 blocks, the modified volinfo block being a modified version of the snapshot volinfo block, wherein the modified volinfo block forms a root of a modified volinfo block buffer tree that is similar to a parent volinfo block buffer tree of the parent vvol such that all blocks of the parent volinfo block buffer tree are accessible when traversing the modified volinfo block buffer tree.

7. The system of claim 6 wherein the shared data structures include file system information (fsinfo) blocks, inodes, indirect blocks and data blocks.

8. The system of claim 7 wherein the file system further executes on the clone to service storage requests directed to the storage system.

9. The system of claim 6 further comprising a parent container file of the parent vvol, the parent container file represented as the parent buffer tree having a plurality of blocks in the aggregate, including level 0 data blocks comprising all blocks used by the parent vvol, wherein one of the level 0 blocks is a volinfo block.

10. The system of claim 9 wherein the snapshot volinfo block is a duplicate copy of the volinfo block.

11. The system of claim 9 further comprising a memory of the storage system organized as a buffer cache configured to store data structures.

12. The system of claim 11 wherein the buffer trees are representations of blocks for files that are loaded into the buffer cache and maintained by the file system.

13. The system of claim 12 wherein each block includes one or more pointers that reference (point to) physical blocks located on the disks.

14. The system of claim 13 wherein the pointers are physical volume block numbers.

15. Apparatus for efficiently creating a copy of a parent virtual volume (vvol) in an aggregate of a storage system, the apparatus comprising:

means for providing a base snapshot of the parent vvol;

means for creating a new vvol embodied as a clone, the clone comprising a container file;

means for modifying a volume information (volinfo) block for the clone, the modified volinfo block comprising a modified version of a volinfo block from the base snapshot;

means for writing the modified volinfo block to the container file; and

means for instantiating the clone to service storage requests directed to the storage system.

16. The apparatus of claim 15 wherein the means for providing comprises one of:

means for generating a snapshot within the parent vvol; and

means for choosing an existing snapshot from the parent vvol.

17. The apparatus of claim 16 wherein the means for instantiating comprises:

means for loading a file system associated with the new vvol onto the clone; and

means for bringing the clone online, with the clone owning only the modified volinfo block.

18. A computer readable medium containing executable program instructions for efficiently creating a copy of a parent virtual volume (vvol) in an aggregate of a storage system, the executable instructions comprising one or more program instructions for:

providing a base snapshot of the parent vvol;

creating a new vvol embodied as a clone, the clone comprising a container file;

modifying a volume information (volinfo) block for the clone, the modified volinfo block comprising a modified version of a volinfo block from the base snapshot;

writing the modified volinfo block to the container file; and

instantiating the clone to service storage requests directed to the storage system.

19. The computer readable medium of claim 18 wherein the program instruction for providing comprises one or more program instructions for one of:

generating a snapshot within the parent vvol; and

choosing an existing snapshot from the parent vvol.

20. The computer readable medium of claim 18 wherein the program instruction for instantiating comprises one or more program instructions for:

loading a file system associated with the new vvol onto the clone; and

bringing the clone online, with the clone owning only the modified volinfo block.