Systems and methods for adaptive copy on write

• US 20090055607A1
• Filed: 08/21/2007
• Published: 02/26/2009
• Est. Priority Date: 08/21/2007
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Schack, Darren P., Lemar, Eric M., Fachan, Neal T.
• Granted Patent: US 7,882,068 B2
• Time in Patent Office: Days
• US Class Current: 711/162
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• 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 16/174 Redundancy elimination performed by the file system management of the data involved in backup or backup restore using de-duplication of the data G06F11/14
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data

Abstract

In one embodiment, a user or client device communicates with a distributed file system comprised of one or more physical nodes. The data on each of the physical nodes store metadata about files and directories within the file system. Some of the embodiments permit a user to take a snapshot of data stored on the file system. The snapshot may include a single file, a single directory, a plurality of files within a directory, a plurality of directories, a path on the file system that includes nested files and subdirectories, or more than one path on the file system that each includes nested files and directories. In some embodiments, systems and methods intelligently choose whether to use copy-on-write or point-in-time copy when saving data in a snapshot version of a file whose current version is being overwritten. In some embodiments, systems and methods allow snapshot users to return from a snapshot directory to the immediate parent directory from which the user entered into the snapshot.

Claims

1. A method of determining whether to use Copy-On-Write (COW) or Point-In-Time-Copy (PITC) for storing multiple versions of at least a portion of a file, comprising:

receiving a request to modify a portion of a file;

determining whether to perform a Point-In-Time-Copy operation;

if it is determined to perform a Point-In-Time-Copy, performing a Point-In-Time Copy operation on the portion of the file; and

if it is determined not to perform a Point-In-Time-Copy, performing a Copy-On-Write operation on the portion of the file.

2. The method of claim 1, wherein the portion of the file is the entire file.

3. The method of claim 1, wherein the request to modify is a request to delete.

4. The method of claim 1, wherein the request to modify is a request to overwrite.

5. The method of claim 1, wherein determining whether to perform a Point-In-Time-Copy comprises determining at least one of the following:

whether a Point-In-Time-Copy may be performed on the portion without significantly affecting read performance of a current version of the file, whether a condition has been specified to use a Point-In-Time-Copy, and whether a Point-In-Time-Copy will fragment the current version of the file.

6. The method of claim 1, wherein the Point-in-Time-Copy operation comprises allocating a new data block assigned to the current version of the file, transferring a corresponding data block from the current version of the file to a previous version of the file, and overwriting the new data block.

7. The method of claim 1, wherein the Copy-On-Write operation comprises allocating a new data block assigned to the previous version of the file, reading a value from a corresponding data block from the current version of the file, writing the value to the new data block, and overwriting the corresponding data block from the current version of the file.

8. The method of claim 1, wherein the determining comprises determining at least one of the following:

whether the entire file is being deleted, whether the entire file is being overwritten, whether any blocks in the file have had a Copy-On-Write operation performed on them already, whether an entire cluster of contiguous blocks is being deleted, and whether an entire cluster of contiguous blocks is being overwritten.

9. The method of claim 8, wherein the number of contiguous blocks is sixteen.

10. The method of claim 1, wherein the determining comprises:

determining whether the portion of the file is the entire file;

if the portion of the file is the entire file, determining whether the entire file is being deleted or overwritten;

if the entire file is being deleted or overwritten, determining whether any blocks of the file have already had a Copy-On-Write operation performed on them; and

if none of the blocks of the file have already had a Copy-On-Write operation performed on them, concluding that a Point-In-Time-Copy operation may be performed on the portion.

11. The method of claim 1, wherein the determining comprises:

if the portion of the file is a contiguous portion of the file, determining whether the contiguous portion is being entirely deleted or overwritten;

if the contiguous portion is being entirely deleted or overwritten, determining whether any blocks of the contiguous portion have already had a Copy-On-Write operation performed on them; and

if none of the blocks of the contiguous portion have already had a Copy-On-Write operation performed on them, concluding that a Point-In-Time-Copy operation may be performed on the contiguous portion.

12. The method of claim 11, wherein the contiguous portion is a sixteen block cluster.

13. A computer-readable medium having instructions stored thereon for determining, when the instructions are executed, whether to use Copy-On-Write (COW) or Point-In-Time-Copy (PITC) for storing multiple versions of at least a portion of a file, the instructions comprising:

receiving a request to modify a portion of a file;

determining whether to perform a Point-In-Time-Copy operation;

if it is determined to perform a Point-In-Time-Copy, performing a Point-In-Time Copy operation on the portion of the file; and

if it is determined not to perform a Point-In-Time-Copy, performing a Copy-On-Write operation on the portion of the file.

14. A storage module having instructions stored thereon for determining, when the instructions are executed, whether to use Copy-On-Write (COW) or Point-In-Time-Copy (PITC) for storing multiple versions of at least a portion of a file, the storage module comprising:

a computer-readable medium having instructions stored thereon;

a processor capable of executing the instructions; and

a memory system for storing a copy of at least a portion of a file according to the instructions executed on the processor;

wherein the instructions comprise;

receiving a request to modify a portion of a file;

determining whether to perform a Point-In-Time-Copy operation;

if it is determined to perform a Point-In-Time-Copy, performing a Point-In-Time Copy operation on the portion of the file; and

if it is determined not to perform a Point-In-Time-Copy, performing a Copy-On-Write operation on the portion of the file.

15. The storage module of claim 14, wherein the portion of the file is the entire file.

16. The storage module of claim 14, wherein the request to modify is a request to delete.

17. The storage module of claim 14, wherein the request to modify is a request to overwrite.

18. The storage module of claim 14, wherein determining whether to perform a Point-In-Time-Copy comprises determining at least one of the following:

whether a Point-In-Time-Copy may be performed on the portion without significantly affecting read performance of a current version of the file, whether a condition has been specified to use a Point-In-Time-Copy, and whether a Point-In-Time-Copy will fragment the current version of the file.

19. The storage module of claim 14, wherein the Point-In-Time-Copy operation comprises allocating a new data block assigned to the current version of the file, transferring a corresponding data block from the current version of the file to a previous version of the file, and overwriting the new data block.

20. The storage module of claim 14, wherein the Copy-On-Write operation comprises allocating a new data block assigned to the previous version of the file, reading a value from a corresponding data block from the current version of the file, writing the value to the new data block, and overwriting the corresponding data block from the current version of the file.

21. The storage module of claim 14, wherein the determining comprises determining at least one of the following:

whether the entire file is being deleted, whether the entire file is being overwritten, whether any blocks in the file have had a Copy-On-Write operation performed on them already, whether an entire cluster of contiguous blocks is being deleted, and whether an entire cluster of contiguous blocks is being overwritten.

22. The storage module of claim 21, wherein the contiguous number of blocks is sixteen.

23. The storage module of claim 14, wherein the determining comprises:

determining whether the portion of the file is the entire file;

if the portion of the file is the entire file, determining whether the entire file is being deleted or overwritten;

if the entire file is being deleted or overwritten, determining whether any blocks of the file have already had a Copy-On-Write operation performed on them; and

if none of the blocks of the file have already had a Copy-On-Write operation performed on them, concluding that a Point-In-Time-Copy operation may be performed on the portion.

24. The storage module of claim 14, wherein the determining comprises:

if the portion of the file is a contiguous portion of the file, determining whether the contiguous portion is being entirely deleted or overwritten;

if the contiguous portion is being entirely deleted or overwritten, determining whether any blocks of the contiguous portion have already had a Copy-On-Write operation performed on them; and

if none of the blocks of the contiguous portion have already had a Copy-On-Write operation performed on them, concluding that a Point-In-Time-Copy operation may be performed on the contiguous portion.

25. The storage module of claim 24, wherein the contiguous portion is a sixteen block cluster.