ACCESSING SNAPSHOTS OF A TIME BASED FILE SYSTEM

• US 20100274764A1
• Filed: 04/22/2009
• Published: 10/28/2010
• Est. Priority Date: 04/22/2009
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Day, Kenneth Fairclough III, Boyd, Kenneth Wayne, Dewey, Douglas William, O'Toole, Christopher Diebold
• Granted Patent: US 8,392,481 B2
• Time in Patent Office: Days
• US Class Current: 707/649
• 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

Abstract

A file system driver stored in a computational device receives a request to provide access to a snapshot of a rewritable file system at a selected point in time, wherein a plurality of tokens corresponding to a plurality of data units are stored in the rewritable file system, and wherein an ordering relationship is maintained among the plurality of tokens. The file system driver determines a token corresponding to the selected point in time based on the ordering relationship. A virtual subdirectory name is generated corresponding to the determined token. A virtual subdirectory is created with the generated virtual subdirectory name, wherein the virtual subdirectory is a subdirectory of a root directory. The snapshot is accessed via the subdirectory.

Claims

1. A method comprising:

receiving, by a file system driver stored in a computational device, a request to provide access to a snapshot of a rewritable file system at a selected point in time, wherein a plurality of tokens corresponding to a plurality of data units are stored in the rewritable file system, and wherein an ordering relationship is maintained among the plurality of tokens;

determining a token corresponding to the selected point in time based on the ordering relationship;

generating a virtual subdirectory name corresponding to the determined token;

creating a virtual subdirectory with the generated virtual subdirectory name, wherein the virtual subdirectory is a subdirectory of a root directory; and

accessing, the snapshot, via the subdirectory.

2. The method of claim 1, wherein the ordering relationship is such that a first token corresponding to a first data unit is of a lesser numerical value in comparison to a second token corresponding to a second data unit, and wherein the first data unit is written at an earlier point in time in comparison to the second data unit.

3. The method of claim 2, further comprising:

receiving a request to perform operations on the snapshot, wherein the request uses a file system interface; and

interpreting the request and providing access to the snapshot via the virtual subdirectory, wherein at least a pointer from the virtual subdirectory to the snapshot stored in the rewritable file system is used to access the snapshot.

4. The method of claim 3, wherein the file system interface to access the snapshot is also used for accessing other files that are not stored by the rewritable file system, wherein no modifications are made within the file system driver to existing file system interfaces that are used by an operating system, and wherein the existing file system interfaces are also used to access other file systems in addition to being used to access the rewritable file system.

5. The method of claim 1, wherein continuous data protection is provided by allowing the rewritable file system to be reverted to any prior point in time, wherein the determining, generating, creating, and accessing are performed by the file system driver, and wherein the file system driver comprises:

a virtual subdirectory generator application that creates the virtual subdirectory;

a virtual subdirectory accessor application that provides access to the snapshot; and

a token to virtual subdirectory mapper data structure that maps tokens to virtual subdirectory names.

15. The article of manufacture of claim 11, wherein continuous data protection is provided by allowing the rewritable file system to be reverted to any prior point in time, wherein the determining, generating, creating, and accessing are performed by the file system driver, and wherein the file system driver comprises:

a virtual subdirectory generator application that creates the virtual subdirectory;

a virtual subdirectory accessor application that provides access to the snapshot; and

a token to virtual subdirectory mapper data structure that maps tokens to virtual subdirectory names.

6. A system, comprising:

a memory;

a processor coupled to the memory, wherein the processor performs operations, the operations comprising;

receiving, by a file system driver, a request to provide access to a snapshot of a rewritable file system at a selected point in time, wherein a plurality of tokens corresponding to a plurality of data units are stored in the rewritable file system, and wherein an ordering relationship is maintained among the plurality of tokens;

determining a token corresponding to the selected point in time based on the ordering relationship;

generating a virtual subdirectory name corresponding to the determined token;

creating a virtual subdirectory with the generated virtual subdirectory name, wherein the virtual subdirectory is a subdirectory of a root directory; and

accessing, the snapshot, via the subdirectory.

7. The system of claim 6, wherein the ordering relationship is such that a first token corresponding to a first data unit is of a lesser numerical value in comparison to a second token corresponding to a second data unit, and wherein the first data unit is written at an earlier point in time in comparison to the second data unit.

8. The system of claim 7, the operations further comprising:

receiving a request to perform operations on the snapshot, wherein the request uses a file system interface; and

interpreting the request and providing access to the snapshot via the virtual subdirectory, wherein at least a pointer from the virtual subdirectory to the snapshot stored in the rewritable file system is used to access the snapshot.

9. The system of claim 8, wherein the file system interface to access the snapshot is also used for accessing other files that are not stored by the rewritable file system, wherein no modifications are made within the file system driver to existing file system interfaces that are used by an operating system, and wherein the existing file system interfaces are also used to access other file systems in addition to being used to access the rewritable file system.

10. The system of claim 6, wherein continuous data protection is provided by allowing the rewritable file system to be reverted to any prior point in time, wherein the determining, generating, creating, and accessing are performed by the file system driver, and wherein the file system driver comprises:

a virtual subdirectory generator application that creates the virtual subdirectory;

a virtual subdirectory accessor application that provides access to the snapshot; and

a token to virtual subdirectory mapper data structure that maps tokens to virtual subdirectory names.

11. An article of manufacture, wherein code stored in the article of manufacture when executed by a computational device causes operations, the operations comprising:

receiving, by a file system driver, a request to provide access to a snapshot of a rewritable file system at a selected point in time, wherein a plurality of tokens corresponding to a plurality of data units are stored in the rewritable file system, and wherein an ordering relationship is maintained among the plurality of tokens;

determining, by the file system driver, a token corresponding to the selected point in time based on the ordering relationship;

generating a virtual subdirectory name corresponding to the determined token;

creating a virtual subdirectory with the generated virtual subdirectory name, wherein the virtual subdirectory is a subdirectory of a root directory; and

accessing, the snapshot, via the subdirectory.

12. The article of manufacture of claim 11, wherein the ordering relationship is such that a first token corresponding to a first data unit is of a lesser numerical value in comparison to a second token corresponding to a second data unit, and wherein the first data unit is written at an earlier point in time in comparison to the second data unit.

13. The article of manufacture of claim 12, the operations further comprising

receiving a request to perform operations on the snapshot, wherein the request uses a file system interface;

and

interpreting the request and providing access to the snapshot via the virtual subdirectory, wherein at least a pointer from the virtual subdirectory to the snapshot stored in the rewritable file system is used to access the snapshot.

14. The article of manufacture of claim 13, wherein the file system interface to access the snapshot is also used for accessing other files that are not stored by the rewritable file system, wherein no modifications are made within the file system driver to existing file system interfaces that are used by an operating system, and wherein the existing file system interfaces are also used to access other file systems in addition to being used to access the rewritable file system.

16. A method for deploying computing infrastructure, comprising integrating computer-readable code into a computing system, wherein the computer-readable code in combination with the computing system is capable of performing:

receiving, by a file system driver, a request to provide access to a snapshot of a rewritable file system at a selected point in time, wherein a plurality of tokens corresponding to a plurality of data units are stored in the rewritable file system, and wherein an ordering relationship is maintained among the plurality of tokens;

determining, by the file system driver, a token corresponding to the selected point in time based on the ordering relationship;

generating a virtual subdirectory name corresponding to the determined token;

creating a virtual subdirectory with the generated virtual subdirectory name, wherein the virtual subdirectory is a subdirectory of a root directory; and

accessing, the snapshot, via the subdirectory.

17. The method for deploying computing infrastructure of claim 16, wherein the ordering relationship is such that a first token corresponding to a first data unit is of a lesser numerical value in comparison to a second token corresponding to a second data unit, and wherein the first data unit is written at an earlier point in time in comparison to the second data unit.

18. The method for deploying computing infrastructure of claim 17, wherein the computer-readable code in combination with the computing system is capable of performing:

receiving a request to perform operations on the snapshot, wherein the request uses a file system interface; and

interpreting the request and providing access to the snapshot via the virtual subdirectory, wherein at least a pointer from the virtual subdirectory to the snapshot stored in the rewritable file system is used to access the snapshot.

19. The method for deploying computing infrastructure of claim 18, wherein the file system interface to access the snapshot is also used for accessing other files that are not stored by the rewritable file system, wherein no modifications are made within the file system driver to existing file system interfaces that are used by an operating system, and wherein the existing file system interfaces are also used to access other file systems in addition to being used to access the rewritable file system.

20. The method for deploying computing infrastructure of claim 16, wherein continuous data protection is provided by allowing the rewritable file system to be reverted to any prior point in time, wherein the determining, generating, creating, and accessing are performed by the file system driver, and wherein the file system driver comprises:

a virtual subdirectory generator application that creates the virtual subdirectory;

a virtual subdirectory accessor application that provides access to the snapshot; and

a token to virtual subdirectory mapper data structure that maps tokens to virtual subdirectory names.