Storage system format for transaction safe file system

• US 20080172426A1
• Filed: 01/16/2007
• Published: 07/17/2008
• 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 7,747,664 B2
• Time in Patent Office: Days
• US Class Current: 707/205
• 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 system comprising:

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

a first file allocation table adapted to store addresses describing chains of storage segments;

a first bitmap image adapted to store an allocation bit for each of said storage segments;

a second file allocation table being a synchronized copy of said first file allocation table;

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

a pointer adapted to indicate that said first file allocation table and said first bitmap image are last known good.

2. The system of claim 1 further comprising:

a processor adapted to;

perform a change to a portion of said file system, said change comprising modifying said second bitmap image;

after said change is completed, modify said pointer to indicate that said second file allocation table and said second bitmap image are last known good; and

update said first file allocation table and said first bitmap image.

3. The system of claim 2 wherein said change comprises deleting at least a portion of a file.

4. The system of claim 2 wherein said change further comprises modifying said second file allocation table.

5. The system of claim 4 wherein said change comprises at least one of a group composed of adding a file and modifying a file.

6. The system of claim 5 wherein said change further comprises:

updating a directory entry to reflect a size change of said file;

updating said second file allocation table to modify a cluster chain; and

updating said second bitmap image to indicate allocated clusters for said file.

7. The system of claim 4 wherein said change comprises:

deleting a first file having a first name and a first place in a directory structure; and

renaming a second file to said first name and said first place in said directory structure.

8. The system of claim 2 wherein said change comprises tracking modifications to said second file allocation table to define modified portions of said second file allocation table, said processor further adapted to changing said modified portions within said first file allocation table.

9. A method comprising:

indicating a first file allocation table as known good, said first file allocation table adapted to store addresses describing chains of storage segments, said storage segments comprised in a file system;

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

synchronizing a second file allocation table to said first file allocation table;

synchronizing a second bitmap image to said first bitmap image;

performing a change to a portion of said file system, said change comprising modifying said second bitmap image;

after said change is completed, indicating that said second file allocation table and said second bitmap image are known good; and

updating said first bitmap image.

10. The method of claim 9 further comprising:

performing a non-transaction safe change to a portion of said file system in a non-transaction safe mode, said non-transaction safe change comprising modifying said first bitmap image.

11. The method of claim 9 wherein said change comprises deleting at least a portion of a file.

12. The method of claim 9 wherein said change further comprises modifying said second file allocation table, said method further comprising updating said first file allocation table.

13. The method of claim 12 wherein said change comprises at least one of a group composed of adding a file and modifying a file.

14. The method of claim 12 wherein said change further comprises:

updating a directory entry to reflect a said of said file;

updating said second file allocation table to modify a cluster chain; and

updating said second bitmap image to indicate allocated clusters for said file.

15. The method of claim 12 wherein said change comprises tracking modifications to said second file allocation table to define modified portions of said second file allocation table, said method further comprising changing said modified portions within said first file allocation table.

16. The method of claim 9 wherein:

said change comprises tracking modifications to said second file allocation table to define modified portions of said second file allocation table; and

said update comprises changing said modified portions within said first file allocation table.

17. A computer readable media comprising computer executable instructions adapted to perform the method of claim 9.

18. A computer file system comprising:

a first file allocation table adapted to store addresses describing chains of storage segments;

a first bitmap image adapted to store an allocation bit for each of said storage segments;

a second file allocation table being a synchronized copy of said first file allocation table;

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

a pointer adapted to indicate that said first file allocation table and said first bitmap image are last known good.

19. A data storage system comprising a computer readable media having data organized in a computer file system of claim 18.

20. A computer readable media comprising computer readable instructions adapted to create the computer file system of claim 18.