Dynamic links to file system snapshots

• US 20030158873A1
• Filed: 02/15/2002
• Published: 08/21/2003
• Est. Priority Date: 02/15/2002
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Sawdon, Wayne A., Schmuck, Frank B.
• Granted Patent: US 7,216,135 B2
• Time in Patent Office: Days
• US Class Current: 707/204
• CPC Class Codes: G06F 16/10 File systems; File servers
• CPC Class Codes: G06F 3/061 Improving I/O performance
• CPC Class Codes: G06F 3/0643 Management of files
• 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: Y10S 707/99931 Database or file accessing
• CPC Class Codes: Y10S 707/99956 File allocation

Abstract

A system, method and computer readable medium for providing dynamic links to file system snapshots is disclosed. A link corresponding to a file system inode is generated. Upon activation of the link, the snapshot identifier of the most recent snapshot is retrieved and the most recent snapshot is identified. If the most recent snapshot includes an inode corresponding to the file system inode and the file system inode includes a disk address, then the data block referenced by the disk address is retrieved. If the most recent snapshot includes an inode corresponding to the file system inode and the file system inode includes a ditto disk address (or the inode corresponding to the file system inode is not included), then the inode corresponding to the file system inode indicated in the link is retrieved and the data block corresponding to the file system inode is retrieved.

Claims

1. A method on a client information processing system for providing access to a snapshot dataset, comprising:

generating a link, wherein the link specifies an inode number of a source file and wherein the link does not specify a snapshot dataset identifier;

retrieving, upon activation of the link, a snapshot identifier corresponding to a most recent snapshot dataset;

identifying the most recent snapshot dataset using the snapshot identifier; and

determining whether the most recent snapshot dataset includes an inode corresponding to the inode number specified in the link.

2. The method of claim 1:

wherein if the most recent snapshot dataset includes an inode corresponding to the inode number specified in the link, then determining whether a disk address in the inode is a ditto disk address;

wherein if the disk address in the inode is not a ditto disk address, then retrieving a data block referenced by the disk address; and

wherein if the disk address in the inode is a ditto disk address, then retrieving a file system inode corresponding to the inode number specified in the link and retrieving a data block referenced by a disk address in the file system inode.

3. The method of claim 1:

wherein if the most recent snapshot dataset does not include an inode corresponding to the inode number specified in the link, then retrieving a file system inode corresponding to the inode number specified in the link and retrieving a data block referenced by a disk address in the file system inode.

4. The method of claim 1:

wherein if the most recent snapshot dataset includes an inode corresponding to the inode number specified in the link, then determining whether a disk address in the inode is a ditto disk address;

wherein if the disk address in the inode is not a ditto disk address, then retrieving an indirect block referenced by the disk address and at least one data block referenced by at least one disk address in the indirect block; and

wherein if the disk address in the inode is a ditto disk address, then retrieving a file system inode corresponding to the inode number specified in the link, retrieving an indirect block referenced by a disk address in the file system inode and retrieving at least one data block referenced by at least one disk address in the indirect block.

5. The method of claim 1:

wherein if the most recent snapshot dataset does not include an inode corresponding to the mode number specified in the link, then retrieving a file system node corresponding to the inode number specified in the link retrieving an indirect block referenced by a disk address in the file system inode and retrieving at least one data block referenced by at least one disk address in the indirect block.

26. The method of claim 1:

wherein if the most recent snapshot dataset includes an inode corresponding to the inode number specified in the link, then determining whether a disk address in the inode references a data block;

wherein if the disk address in the inode references a data block, then retrieving the data block referenced by the disk address; and

wherein if the disk address in the inode does not reference a data block but instead a second inode, then retrieving the second inode and retrieving a data block referenced by a disk address in the second inode.

27. The method of claim 1, wherein the generating step comprises:

generating a link for each source file associated with a most recent snapshot dataset, wherein each link specifies an inode number of a source file and wherein each link does not specify a snapshot dataset identifier.

6. A method on a client information processing system for providing access to a snapshot dataset, comprising:

generating a directory including a subdirectory entry for each snapshot of a source file, wherein each subdirectory entry includes a link to a snapshot of the source file;

retrieving, upon an access request into the directory, a subdirectory entry corresponding to a most recent snapshot of the source file; and

providing, from the retrieved subdirectory entry, a link to a snapshot of the source file.

7. The method of claim 6, wherein the providing from the retrieved subdirectory entry includes a link specifying an inode corresponding to a snapshot of the source file.

8. A system on a client information processing system for providing access to a snapshot dataset, comprising:

means for generating a link, wherein the link specifies an inode number of a source file and wherein the link does not specify a snapshot dataset identifier;

means for retrieving, upon activation of the link, a snapshot identifier corresponding to a most recent snapshot dataset;

means for identifying the most recent snapshot dataset using the snapshot identifier; and

means for determining whether the most recent snapshot dataset includes an inode corresponding to the inode number specified in the link.

9. The system of claim 8, further comprising:

means for determining whether a disk address in the inode is a ditto disk address;

means for retrieving a data block referenced by the disk address; and

means for retrieving a file system inode corresponding to the inode number specified in the link and retrieving a data block referenced by a disk address in the file system inode.

10. The system of claim 8, further comprising:

means for retrieving a file system inode corresponding to the inode number specified in the link and retrieving a data block referenced by a disk address in the file system inode.

11. The system of claim 8, further comprising:

means for determining whether a disk address in the inode is a ditto disk address;

means for retrieving an indirect block referenced by the disk address and at least one data block referenced by at least one disk address in the indirect block; and

means for retrieving a file system inode corresponding to the inode number specified in the link, retrieving an indirect block referenced by a disk address in the file system inode and retrieving at least one data block referenced by at least one disk address in the indirect block.

12. The system of claim 8, further comprising:

means for retrieving a file system inode corresponding to the inode number specified in the link, retrieving an indirect block referenced by a disk address in the file system inode and retrieving at least one data block referenced by at least one disk address in the indirect block.

13. A system on a client information processing system for providing access to a snapshot dataset, comprising:

means for generating a directory including a subdirectory entry for each snapshot of a source file, wherein each subdirectory entry includes a link to a snapshot of the source file;

means for retrieving, upon an access request into the directory, a subdirectory entry corresponding to a most recent snapshot of the source file; and

means for providing, from the retrieved subdirectory entry, a link to a snapshot of the source file.

14. The system of claim 13, wherein means for providing from the retrieved subdirectory entry includes a link specifying an inode corresponding to a snapshot of the source file.

15. A computer readable medium on a client information processing system including computer instructions for providing access to a snapshot dataset, the computer instructions comprising instructions for:

generating a link, wherein the link specifies an inode number of a source file and wherein the link does not specify a snapshot dataset identifier;

retrieving, upon activation of the link, a snapshot identifier corresponding to a most recent snapshot dataset;

identifying the most recent snapshot dataset using the snapshot identifier; and

determining whether the most recent snapshot dataset includes an inode corresponding to the inode number specified in the link.

16. The computer readable medium of claim 15, the computer instructions further comprising instructions for:

wherein if the most recent snapshot dataset includes an inode corresponding to the inode number specified in the link, then determining whether a disk address in the inode is a ditto disk address;

wherein if the disk address in the inode is not a ditto disk address, then retrieving a data block referenced by the disk address; and

wherein if the disk address in the inode is a ditto disk address, then retrieving a file system inode corresponding to the inode number specified in the link and retrieving a data block referenced by a disk address in the file system inode.

17. The computer readable medium of claim 15, the computer instructions further comprising instructions for:

wherein if the most recent snapshot dataset does not include an inode corresponding to the inode number specified in the link, then retrieving a file system inode corresponding to the inode number specified in the link and retrieving a data block referenced by a disk address in the file system inode.

18. The computer readable medium of claim 15, the computer instructions further comprising instructions for:

wherein if the most recent snapshot dataset includes an inode corresponding to the inode number specified in the link, then determining whether a disk address in the inode is a ditto disk address;

wherein if the disk address in the inode is not a ditto disk address, then retrieving an indirect block referenced by the disk address and at least one data block referenced by at least one disk address in the indirect block; and

wherein if the disk address in the inode is a ditto disk address, then retrieving a file system inode corresponding to the inode number specified in the link, retrieving an indirect block referenced by a disk address in the file system inode and retrieving at least one data block referenced by at least one disk address in the indirect block.

19. The computer readable medium of claim 15, the computer instructions further comprising instructions for:

wherein if the most recent snapshot dataset does not include an inode corresponding to the inode number specified in the link, then retrieving a file system inode corresponding to the inode number specified in the link retrieving an indirect block referenced by a disk address in the file system inode and retrieving at least one data block referenced by at least one disk address in the indirect block.

20. A computer readable medium on a client information processing system including computer instructions for providing access to a snapshot dataset, the computer instructions comprising instructions for:

generating a directory including a subdirectory entry for each snapshot of a source file, wherein each subdirectory entry includes a link to a snapshot of the source file;

retrieving, upon an access request into the directory, a subdirectory entry corresponding to a most recent snapshot of the source file; and

providing, from the retrieved subdirectory entry, a link to a snapshot of the source file.

21. A system on a client information processing system for providing access to a snapshot dataset, comprising:

a link, wherein the link specifies an inode number of a source file and wherein the link does not specify a snapshot dataset identifier;

a snapshot identifier corresponding to a most recent snapshot dataset, wherein the snapshot identifier is retrieved upon activation of the link,

means for identifying the most recent snapshot dataset using the snapshot identifier; and

an inode corresponding to the inode number specified in the link, wherein the inode is included in the most recent snapshot dataset.

22. The system of claim 21, further comprising:

a disk address included in the inode;

a data block referenced by the disk address;

a file system inode corresponding to the inode number specified in the link; and

a data block referenced by a disk address in the file system inode.

23. The system of claim 21, further comprising:

a file system inode corresponding to the inode number specified in the link; and

a data block referenced by a disk address in the file system inode.

24. A system on a client information processing system for providing access to a snapshot dataset, comprising:

a directory including a subdirectory entry for each snapshot of a source file, wherein each subdirectory entry includes a link to a snapshot of the source file;

a subdirectory entry corresponding to a most recent snapshot of the source file, wherein the subdirectory entry is retrieved upon an access request into the directory; and

a link to a snapshot of the source file, wherein the link is provided by the retrieved subdirectory entry.

25. The system of claim 24, wherein the retrieved subdirectory entry includes a link specifying an inode corresponding to a snapshot of the source file.