ERASE COUNT RECOVERY

• US 20090198869A1
• Filed: 01/31/2008
• Published: 08/06/2009
• Est. Priority Date: 01/31/2008
• Status: Active Grant

• Current Assignee: SanDisk IL Ltd. (Western Digital Corporation)
• Original Assignee: SanDisk IL Ltd. (Western Digital Corporation)
• Inventors: Mosek, Amir
• Granted Patent: US 7,925,822 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/7211 Wear leveling

Abstract

An erase count of a flash memory block which is lost, e.g., due to power failure is updated or replaced by using known erase counts of other blocks of the flash memory. A flash management algorithm assigns a new erase count value instead of the lost one based on either a maximum value, an average value or a value combining the maximum value of the known erase counts and some tolerance value. The known values may be obtained from wear leveling data or from a stored erase history.

Claims

1. A method of updating a lost or invalid erase count of a given block of a flash memory, the method comprising the steps of:

a. obtaining a new erase count for a given block of a flash memory, using known erase counts of other blocks of the flash memory; and

b. assigning the new erase count to the given block.

2. The method of claim 1, wherein the step of obtaining includes calculating an average value of the known erase counts and setting the new erase count to the average value.

3. The method of claim 1, wherein the step of obtaining includes determining a maximum value of the known erase counts and setting the new erase count to the maximum value.

4. The method of claim 1, wherein the step of obtaining includes determining a maximum value of the known erase counts and setting the new erase count to a sum of the obtained maximum value and a value of an erase count tolerance.

5. The method of claim 2, wherein the calculating an average value includes calculating an average value using a wear-leveling algorithm.

6. The method of claim 2, wherein the calculating an average value includes calculating an average value using an erase history.

7. The method of claim 5, wherein the wear leveling algorithm is run on a platform selected from the group consisting of a flash memory device, a host device and a network server.

8. The method of claim 3, wherein the determining a maximum value includes determining a maximum value using a wear-leveling algorithm.

9. The method of claim 3, wherein the determining a maximum value includes determining a maximum value using an erase history.

10. The method of claim 8, wherein the wear leveling algorithm is run on a platform selected from the group consisting of a flash memory device, a host device and a network server.

11. The method of claim 4, wherein the determining a maximum value includes determining a maximum value using a wear-leveling algorithm.

12. The method of claim 4, wherein the determining a maximum value includes determining a maximum value using an erase history.

13. The method of claim 1, wherein the wear leveling algorithm is run on a platform selected from the group consisting of a flash memory device, a host device and a network server.

14. The method of claim 1, wherein the step of obtaining is performed in response to a power failure due to which a previous erase count of the given block is lost.

15. A computer readable storage medium having computer readable code embodied in the computer readable storage medium, the computer readable code comprising instructions for updating a lost or invalid erase count of a given block of a flash memory, by:

a) obtaining a new erase count for a given block of a flash memory, using known erase counts of other blocks of the flash memory; and

b) assigning the new erase count to the given block.

16. The computer readable storage medium of claim 15, wherein the obtaining a new erase count for a given block of a flash memory using known erase counts of other blocks of the flash memory includes calculating an average value of the known erase counts, and wherein the assigning the new erase count to the given block includes setting the new erase count to the average value.

17. The computer readable storage medium of claim 15, wherein the obtaining a new erase count for a given block of a flash memory using known erase counts of other blocks of the flash memory includes determining a maximum value of the known erase counts, and wherein the assigning the new erase count to the given block includes setting the new erase count to the maximum value.

18. The computer readable storage medium of claim 15, wherein the obtaining a new erase count for a given block of a flash memory using known erase counts of other blocks of the flash memory includes determining a maximum value of the known erase counts, and wherein the assigning the new erase count to the given block includes setting the new erase count to a sum of the determined maximum value and a value of an erase count tolerance.

19. The computer readable storage medium of claim 16, wherein the calculating an average value includes calculating an average value using a wear-leveling algorithm.

20. The computer readable storage medium of claim 16, wherein the calculating an average value includes calculating an average value using an erase history.

21. The computer readable storage medium of claim 19, wherein the wear leveling algorithm is run on a platform selected from the group consisting of a flash memory device, a host device and a network server.

22. The computer readable storage medium of claim 17, wherein the determining a maximum value includes determining a maximum value using a wear-leveling algorithm.

23. The computer readable storage medium of claim 17, wherein the determining a maximum value includes determining a maximum value using an erase history.

24. The computer readable storage medium of claim 22, wherein the wear leveling algorithm is run on a platform selected from the group consisting of a flash memory device, a host device and a network server.

25. The computer readable storage medium of claim 18, wherein the determining a maximum value includes determining a maximum value using a wear-leveling algorithm.

26. The computer readable storage medium of claim 18, wherein the determining a maximum value includes determining a maximum value using an erase history.

27. The computer readable storage medium of claim 26, wherein the wear leveling algorithm is run on a platform selected from the group consisting of a flash memory device, a host device and a network server.

28. The computer readable storage medium of claim 15, wherein the obtaining a new erase count for a given block of a flash memory using known erase counts of other blocks of the flash memory is performed in response to a power failure due to which a previous erase count of the given block is lost.