Method and system for implementing writable snapshots in a virtualized storage environment

• US 9,009,106 B1
• Filed: 08/10/2011
• Issued: 04/14/2015
• Est. Priority Date: 08/10/2011
• Status: Active Grant

• Current Assignee: Nutanix Incorporated
• Original Assignee: Nutanix Incorporated
• Inventors: Aron, Mohit, Byrne, Brian
• Primary Examiner(s): Kim, Taelor
• Application Number:
  US13/207,371
• Time in Patent Office: 1,343 Days
• Field of Search: None
• US Class Current: 707/610
• CPC Class Codes: G06F 11/14 Error detection or correction of the data by redundancy in operation G06F11/16 takes precedence
• CPC Class Codes: G06F 12/12 Replacement control
• CPC Class Codes: G06F 16/00 Information retrieval; Database structures therefor; File system structures therefor
• CPC Class Codes: G06F 16/128 Details of file system snapshots on the file-level, e.g. snapshot creation, administration, deletion use of snapshots for error detection or correction G06F11/14, G06F11/16
• CPC Class Codes: G06F 16/182 Distributed file systems
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data
• CPC Class Codes: G06F 3/0611 in relation to response time
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/0626 Reducing size or complexity of storage systems
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]
• CPC Class Codes: G06F 3/0683 Plurality of storage devices

Abstract

Disclosed is an improved approach for implementing and maintaining writable snapshots. An efficient approach is provided for implementing snapshots that can be used to immediately create snapshots without incurring any detectable delays in providing access to the new snapshots. Also described are improved metadata structures that can be used to implement and maintain the writable snapshots.

Claims

1. A computer-implemented method for implementing a writable snapshot that is performed using a processor, comprising:

identifying a parent snapshot;

creating a child snapshot, in which the child snapshot is to be accessed in place of the parent snapshot without immediately copying all of the contents of the parent snapshot to the child snapshot;

and creating a writable child snapshot, in which modifications can be made to the content of the writable snapshot and in which the writable snapshot can be accessed without immediately copying all of the contents of the parent snapshot to the writable snapshot, in which future data requests for the parent snapshot are directed to the child snapshot,

in which a data request is made for a portion of the child snapshot or the writable snapshot which has not been copied from the parent snapshot and in which the data request is redirected to the parent snapshot,

in which a data item is copied from the parent snapshot to the child snapshot or the writable snapshot upon a need to access the data item in the child snapshot or the writable snapshot in which a data item is copied from the parent snapshot to the child snapshot or the writable snapshot upon a need to access the data item in the child snapshot or the writable snapshot,

in which a first portion of the data item exists in the writable snapshot and a second portion of the data item is referenced to the parent snapshot,

in which metadata is used to track referencing between the child snapshot and the parent snapshot.

2. The method of claim 1 in which the data request for a block within the child snapshot or the writable snapshot, and identification of the block not existing in the child snapshot or the writable snapshot prompts the data request to be redirected to the block in the parent snapshot.

3. The method of claim 1 in which the need to access the data item is prompted by a request to update or modify the data item in the writable snapshot.

4. The method of claim 1 in which a data item is copied from the parent snapshot to the child snapshot or the writable snapshot during periods of low system activity.

5. The method of claim 1 in which snapshots are implemented as virtual disks.

6. The method of claim 1 in which multiple hierarchies of parent and child snapshots are created.

7. The method of claim 1 in which the parent snapshot is deleted after the contents of the parent snapshot are no longer needed.

8. The method of claim 1 in which the writable snapshot is created in a virtualized system, and the writable snapshot corresponds to a virtual storage entity.

9. The method of claim 8 in which metadata is employed for the virtualization system, wherein the metadata comprises a first map corresponding to virtual disks, a second map corresponding to extent identifiers, and a third map corresponding to groups of extents, and the writable snapshot corresponds to entries within the metadata.

10. The method of claim 9 in which the writable snapshot corresponds to an extent group, and an entry is made in the third map that corresponds to the extent group for the writable snapshot.

11. The method of claim 9 in which the writable snapshot corresponds to an extent group, and an entry is made in the first map that corresponds an identifier for the extent group to a virtual disk name for the writable snapshot.

12. The method of claim 9 in which the writable snapshot corresponds to an extent group, and an entry is made in the second map that corresponds an identifier for the extent group for the writable snapshot.

13. The method of claim 9 in which the metadata is copied to the writable snapshot from the parent snapshot instead of actual data.

14. The method of claim 9 in which a tentative update message is made to the metadata upon an intent to modify the metadata.

15. A system for implementing a writable snapshot, comprising:

a processor to handle computing instructions to access the storage devices; and

computer readable medium comprising executable code that is executable by the processor for identifying a parent snapshot, creating a child snapshot, in which the child snapshot is to be accessed in place of the parent snapshot without immediately copying all of the contents of the parent snapshot to the child snapshot, and creating a writable child snapshot, in which modifications can be made to the content of the writable snapshot and in which the writable snapshot can be accessed without immediately copying all of the contents of the parent snapshot to the writable snapshot, in which future data requests for the parent snapshot are directed to the child snapshot,

in which a data request is made for a portion of the child snapshot or the writable snapshot which has not been copied from the parent snapshot and in which the data request is redirected to the parent snapshot,

in which a data item is copied from the parent snapshot to the child snapshot or the writable snapshot upon a need to access the data item in the child snapshot or the writable snapshot,

in which a first portion of the data item exists in the writable snapshot and a second portion of the data item is referenced to the parent snapshot,

in which metadata is used to track referencing between the child snapshot and the parent snapshot.

16. The system of claim 15 in which the data request for a block within the child snapshot or the writable snapshot, and identification of the block not existing in the child snapshot or the writable snapshot prompts the data request to be redirected to the block in the parent snapshot.

17. The system of claim 15 in which the need to access the data item is prompted by a request to update or modify the data item in the writable snapshot.

18. The system of claim 15 in which a data item is copied from the parent snapshot to the child snapshot or the writable snapshot during periods of low system activity.

19. The system of claim 15 in which snapshots are implemented for virtual disks.

20. The system of claim 15 in which multiple hierarchies of parent and child snapshots are created.

21. The system of claim 15 in which the parent snapshot is deleted after the contents of the parent snapshot are no longer needed.

22. The system of claim 15 in which the writable snapshot is created in a virtualization system, and the writable snapshot corresponds to a virtual storage entity.

23. The system of claim 22 in which metadata is employed for the virtualization system, wherein the metadata comprises a first map corresponding to virtual disks, a second map corresponding to extent identifiers, and a third map corresponding to groups of extents, and the writable snapshot corresponds to entries within the metadata.

24. The system of claim 23 in which the writable snapshot corresponds to an extent group, and an entry is made in the third map that corresponds to the extent group for the writable snapshot.

25. The system of claim 23 in which the writable snapshot corresponds to an extent group, and an entry is made in the first map that corresponds an identifier for the extent group to a virtual disk name for the writable snapshot.

26. The system of claim 23 in which the writable snapshot corresponds to an extent group, and an entry is made in the second map that corresponds an identifier for the extent group for the writable snapshot.

27. The system of claim 23 in which the metadata is copied to the writable snapshot from the parent snapshot instead of actual data.

28. The system of claim 23 in which a tentative update message is made to the metadata upon an intent to modify the metadata.

29. A computer program product embodied on a non-transitory computer readable medium, the computer readable medium having stored thereon a sequence of instructions which, when executed by a processor causes the processor to execute a method for implementing a writable snapshot, the method comprising:

identifying a parent snapshot;

creating a child snapshot, in which the child snapshot is to be accessed in place of the parent snapshot without immediately copying all of the contents of the parent snapshot to the child snapshot; and

creating a writable child snapshot, in which modifications can be made to the content of the writable snapshot and in which the writable snapshot can be accessed without immediately copying all of the contents of the parent snapshot to the writable snapshot, in which future data requests for the parent snapshot are directed to the child snapshot,

in which a data request is made for a portion of the child snapshot or the writable snapshot which has not been copied from the parent snapshot and in which the data request is redirected to the parent snapshot,

in which a data item is copied from the parent snapshot to the child snapshot or the writable snapshot upon a need to access the data item in the child snapshot or the writable snapshot,

in which a first portion of the data item exists in the writable snapshot and a second portion of the data item is referenced to the parent snapshot,

in which metadata is used to track referencing between the child snapshot and the parent snapshot.

30. The computer program product of claim 29 in which the data request for a block within the child snapshot or the writable snapshot, and identification of the block not existing in the child snapshot or the writable snapshot prompts the data request to be redirected to the block in the parent snapshot.

31. The computer program product of claim 29 in which the need to access the data item is prompted by a request to update or modify the data item in the writable snapshot.

32. The computer program product of claim 29 in which a data item is copied from the parent snapshot to the child snapshot or the writable snapshot during periods of low system activity.

33. The computer program product of claim 29 in which snapshots are implemented as virtual disks.

34. The computer program product of claim 29 in which multiple hierarchies of parent and child snapshots are created.

35. The computer program product of claim 29 in which the parent snapshot is deleted after the contents of the parent snapshot are no longer needed.

36. The computer program product of claim 29 in which the writable snapshot is created in a virtualization system, and the writable snapshot corresponds to a virtual storage entity.

37. The computer program product of claim 36 in which metadata is employed for the virtualization system, wherein the metadata comprises a first map corresponding to virtual disks, a second map corresponding to extent identifiers, and a third map corresponding to groups of extents, and the writable snapshot corresponds to entries within the metadata.

38. The computer program product of claim 37 in which the writable snapshot corresponds to an extent group, and an entry is made in the third map that corresponds to the extent group for the writable snapshot.

39. The computer program product of claim 37 in which the writable snapshot corresponds to an extent group, and an entry is made in the first map that corresponds an identifier for the extent group to a virtual disk name for the writable snapshot.

40. The computer program product of claim 37 in which the writable snapshot corresponds to an extent group, and an entry is made in the second map that corresponds an identifier for the extent group for the writable snapshot.

41. The computer program product of claim 37 in which the metadata is copied to the writable snapshot from the parent snapshot instead of actual data.

42. The computer program product of claim 37 in which a tentative update message is made to the metadata upon an intent to modify the metadata.