Read disturb effect determination

• US 8,930,778 B2
• Filed: 11/15/2012
• Issued: 01/06/2015
• Est. Priority Date: 11/15/2012
• Status: Expired due to Fees

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Cohen, Earl T.
• Primary Examiner(s): Rizk, Sam
• Application Number:
  US13/677,938
• Publication Number:
  US 20140136883A1
• Time in Patent Office: 782 Days
• Field of Search: 714/5, 714/704, 714/773, 711/165
• US Class Current: 714/704
• CPC Class Codes: G06F 11/2094 Redundant storage or storage space G06F11/2056 takes precedence
• CPC Class Codes: G11C 16/3422 Circuits or methods to evaluate read or write disturbance in nonvolatile memory, without steps to mitigate the problem
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles

Abstract

An apparatus comprising a non-volatile memory and a controller. The controller is coupled to the non-volatile memory and configured to (i) accumulate a read disturb count for a first region of the non-volatile memory, (ii) accumulate error statistics for a second region of the non-volatile memory, (iii) determine, based upon both the read disturb count and the error statistics, whether the first region has reached a read disturb limit, and (iv) in response to determining that the first region has reached the read disturb limit, relocate at least some data of the first region.

Claims

1. An apparatus comprising:

a non-volatile memory; and

a controller coupled to said non-volatile memory and configured to (i) accumulate a read disturb count for a first region of said non-volatile memory, (ii) accumulate error statistics for a second region of said non-volatile memory, and (iii) determine, based upon both the read disturb count and the error statistics, whether the first region has reached a read disturb limit, wherein in response to determining that the first region has not reached the read disturb limit, said controller adjusts the accumulated read disturb count based upon the error statistics, and in response to determining that the first region has reached the read disturb limit, the controller relocates at least some data of the first region.

2. The apparatus according to claim 1, wherein the second region is the same as the first region.

3. The apparatus according to claim 1, wherein the first region is an integer number of blocks of the non-volatile memory.

4. The apparatus according to claim 1, wherein the controller increments the read disturb count for each read of a page of the non-volatile memory within the first region.

5. The apparatus according to claim 1, wherein the controller is further configured to adjust the read disturb count based at least in part upon the error statistics when the read disturb count reaches a read disturb count threshold.

6. The apparatus according to claim 1, wherein the controller is further configured to compute a maximum percentage of an error correcting ability used in correcting data read from the second region.

7. The apparatus according to claim 6, wherein each of a plurality of sub-regions of the second region uses a different error correction code rate.

8. The apparatus according to claim 1, wherein the controller is configured to determine whether the first region has reached the read disturb limit by comparing the read disturb count to a read disturb count threshold and comparing the error statistics to an error statistics threshold.

9. The apparatus according to claim 1, wherein the controller is further configured to (i) clear the read disturb count in response to erasing the first region and (ii) reset the error statistics in response to erasing the second region.

10. A method of read disturb effect determination comprising the steps of:

accumulating a read disturb count for a first region of a non-volatile memory;

accumulating error statistics for a second region of the non-volatile memory;

determining, based upon both the read disturb count and the error statistics, whether the first region has reached a read disturb limit;

in response to determining that the first region has not reached the read disturb limit, adjusting the accumulated read disturb count based upon the error statistics; and

in response to determining that the first region has reached the read disturb limit, relocating at least some data of the first region.

11. The method according to claim 10, wherein the second region is the same as the first region.

12. The method according to claim 10, wherein the first region is an integer number of blocks of the non-volatile memory.

13. The method according to claim 10, wherein the step of accumulating the read disturb count comprises incrementing the read disturb count for each read of a page of the non-volatile memory within the first region.

14. The method according to claim 10, wherein the step of accumulating the read disturb count further comprises adjusting the read disturb count based at least in part upon the error statistics when the read disturb count reaches a read disturb count threshold.

15. The method according to claim 10, wherein the step of accumulating the error statistics comprises computing a maximum percentage of an error correcting ability used in correcting data read from the second region.

16. The method according to claim 15, wherein each of a plurality of sub-regions of the second region uses a different error correction code rate.

17. The method according to claim 10, wherein the step of determining whether the first region has reached the read disturb limit comprises comparing the read disturb count to a read disturb count threshold and comparing the error statistics to an error statistics threshold.

18. The method according to claim 10, further comprising:

in response to erasing the first region, clearing the read disturb count.

19. The method according to claim 10, further comprising:

in response to erasing the second region, resetting the error statistics.

20. The method according to claim 10, wherein the data of the first region that is relocated is active data of the first region.