STORAGE SYSTEM FORMAT FOR TRANSACTION SAFE FILE SYSTEM

• US 20100217788A1
• Filed: 05/06/2010
• Published: 08/26/2010
• Est. Priority Date: 01/16/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Rogers, Andrew, Patel, Sachin, Gopalan, Yadhu
• Granted Patent: US 8,001,165 B2
• Time in Patent Office: Days
• US Class Current: 707/826
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata

Abstract

A transaction safe file system uses two sets of file allocation tables and bitmap images to perform file modifications on one of the sets while the other set remains a last known good set. After a modification is complete, a pointer is changed to the newly modified set, and the newly modified set becomes the last known good set. The sets are then synchronized. The file allocation table is used to define cluster chains while the bitmap image is used to determine if a cluster is free or not. In some operations, only the bitmap image may need to be manipulated. The file system may be used in a transaction safe mode as well as a non-transaction safe mode.

Claims

1. A method comprising:

indicating a first bitmap image as known good, said first bitmap image adapted to store an allocation bit for storage segments comprised in a file system;

synchronizing a second bitmap image to said first bitmap image;

performing a change to a portion of said file system, said change comprising deleting a file of the file system, wherein deleting the file of the file system does not require a change to a file allocation table of the file system;

modifying said second bitmap image as a result of deleting the file;

after said change is completed, indicating that said second bitmap image is known good; and

synchronizing said first bitmap image to said second bitmap.

2. The method of claim 1, wherein the allocation bit for a particular storage segment identifying whether the particular storage segment is free or not.

3. The method of claim 1, wherein indicating the first bitmap image as known good comprises an atomic change of a single flag.

4. The method of claim 1, wherein indicating the first bitmap image as known good comprises toggling an indicium to the first bitmap image.

5. The method of claim 1, wherein a contiguous indicium is associated with the file, wherein the contiguous indicium indicates when the storage segments assigned to the file are contiguous.

6. The method of claim 1, further comprising performing a non-transaction safe change to a portion of said file system in a non-transaction safe mode.

7. The method of claim 1, further comprising performing a transaction safe change to a portion of said file system in a transaction safe mode.

8. The method of claim 1, wherein a storage segment is a cluster of the file system.

15. The computer-readable storage medium of claim 1, further comprising performing a transaction safe change to a portion of said file system in a transaction safe mode.

16. The computer-readable storage medium of claim 1, wherein a contiguous bit is associated with the file, wherein the contiguous bit indicates when the clusters assigned to the file are contiguous.

9. A computer-readable storage medium comprising computer executable instructions encoded thereon that perform acts comprising:

indicating a first bitmap image as known good, said first bitmap image to indicate cluster usage of clusters comprised in a file system;

synchronizing a second bitmap image to said first bitmap image;

deleting a file of the file system, wherein deleting the file does not require a change to a file allocation table of the file system;

modifying said second bitmap image as a result of deleting the file;

after said change is completed, indicating that said second bitmap image is known good; and

synchronizing said first bitmap image to said second bitmap.

10. The computer-readable storage medium of claim 9, wherein the allocation bit for a particular cluster identifying whether the particular cluster is free or not.

11. The computer-readable storage medium of claim 9, wherein indicating the first bitmap image as known good comprises an atomic change of a single flag.

12. The computer-readable storage medium of claim 9, wherein indicating the first bitmap image as known good comprises toggling an indicium to the first bitmap image.

13. The computer-readable storage medium of claim 9, wherein modifying said second bitmap image comprises changing an allocation bit associated with each cluster of the file to indicate that each cluster is free.

14. The computer-readable storage medium of claim 9, further comprising performing a non-transaction safe change to a portion of said file system in a non-transaction safe mode.

17. A computing device, comprising:

a data storage device having a file system, the file system comprising;

a first bitmap image to indicate whether each cluster of the file system is used or unused;

a second bitmap image being a synchronized identical copy of said first bitmap image;

a processor adapted to;

perform a change to a portion of said file system, said change comprising deleting a file of the file system, wherein deleting the file does not require a change to a file allocation table of the file system;

modify said second bitmap image as a result of deletion of the file;

after said change is completed, indicate that said second bitmap image is known good; and

synchronize said first bitmap image to said second bitmap.

18. The computing device of claim 17, wherein the first and second bitmaps comprise an allocation bit corresponding to each cluster of the file system, wherein a state of each allocation bit indicates whether the corresponding cluster is free or not.

19. The computing device of claim 17, wherein modifying said second bitmap image comprises changing an allocation bit associated with each cluster of the file to indicate that each cluster is free.

20. The computing device of claim 17, wherein a contiguous bit is associated with the file, wherein the contiguous bit indicates when the clusters assigned to the file are contiguous.