Flash storage device with read disturb mitigation

• US 9,098,416 B2
• Filed: 04/21/2014
• Issued: 08/04/2015
• Est. Priority Date: 05/12/2009
• Status: Active Grant

• Current Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Original Assignee: HGST Technologies Santa Ana, Inc. (Western Digital Corporation)
• Inventors: Mataya, Richard A., Hsueh, Po-Jen, Moshayedi, Mark
• Primary Examiner(s): NGUYEN, STEVE N
• Application Number:
  US14/257,978
• Publication Number:
  US 20140223244A1
• Time in Patent Office: 470 Days
• Field of Search: 714/745
• US Class Current: 1/1
• CPC Class Codes: G06F 11/076 by exceeding a count or rate limit, e.g. word- or bit count limit
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/0284 Multiple user address space allocation, e.g. using different base addresses interprocessor communication G06F15/163
• CPC Class Codes: G06F 12/0833 in combination with broadcast means (e.g. for invalidation or updating)
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 12/1009 using page tables, e.g. page table structures
• CPC Class Codes: G06F 2212/2022 Flash memory
• CPC Class Codes: G06F 2212/466 Metadata, control data
• CPC Class Codes: G06F 2212/62 Details of cache specific to multiprocessor cache arrangements
• CPC Class Codes: G06F 2212/7208 Multiple device management, e.g. distributing data over multiple flash devices
• CPC Class Codes: G06F 2212/7209 Validity control, e.g. using flags, time stamps or sequence numbers
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles

Abstract

A method for managing a flash storage device includes initiating a read request and reading requested data from a first storage block of a plurality of storage blocks in the flash storage device based on the read request. The method further includes incrementing a read count for the first storage block and moving the data in the first storage block to an available storage block of the plurality of storage blocks when the read count reaches a first threshold value.

Claims

1. A method for managing a flash storage device, the method comprising the steps of:

initiating a read request;

reading requested data from a first storage block of a plurality of storage blocks in the flash storage device based on the read request, wherein each of the plurality of storage blocks comprises multiple pages, the plurality of storage blocks in the flash storage device are organized into a plurality of zones, each zone comprises at least two storage blocks of the plurality of storage blocks, each storage block has a respective read count, and the first storage block is included in a first zone of the plurality of zones;

incrementing the read count for the first storage block;

determining that the read count for the first storage block has reached a first threshold value;

in response to the determination;

moving the data in the first storage block to an available storage block of the plurality of storage blocks; and

backing up the read counts for each storage block in the first zone to a non-volatile memory in the flash storage device;

determining that the read count of at least one of the storage blocks in a second zone of the plurality of zones has reached a second threshold value less than the first threshold value; and

backing up the read counts for each storage block in the second zone to the non-volatile memory, in response to determining that the read count of at least one of the storage blocks in the second zone has reached the second threshold value.

2. The method of claim 1, further comprising maintaining the read count for each of the plurality of storage blocks in the flash storage device containing data.

3. The method of claim 2, wherein maintaining the read count for each of the plurality of storage blocks containing data comprises storing the read counts in a random access memory in the flash storage device.

4. The method of claim 2, wherein the random access memory comprises a dynamic random access memory.

5. The method of claim 2, wherein maintaining the read count for each of the plurality of storage blocks containing data further comprises storing the read counts in the non-volatile memory in the flash storage device when the flash storage device is powered down.

6. The method of claim 2, wherein maintaining the read count for each of the plurality of storage blocks containing data further comprises storing the read counts in the non-volatile memory in the flash storage device at a predetermined interval.

7. The method of claim 1, further comprising:

performing a read check on the requested data stored in the first storage block; and

moving the data in the first storage block to an available storage block of the plurality of storage blocks when the read check fails.

8. The method of claim 7, wherein performing the read check comprises verifying the data stored in the first storage block using an error-correcting code in the stored data, and wherein the read check fails when an error count in the read-checked data is greater than a safety count.

9. The method of claim 1, wherein the available storage block is an erased storage block.

10. The method of claim 1, wherein the available storage block is a second storage block of the plurality of storage blocks having a read count less than the first threshold value.

11. A flash storage device comprising:

a flash memory; and

a controller configured to;

initiate a read request;

read requested data from a first storage block of a plurality of storage blocks in the flash storage device based on the read request, wherein each of the plurality of storage blocks comprises multiple pages, the plurality of storage blocks in the flash storage device are organized into a plurality of zones, each zone comprises at least two storage blocks of the plurality of storage blocks, each storage block has a respective read count, and the first storage block is included in a first zone of the plurality of zones;

increment the read count for the first storage block;

determine that the read count for the first storage block has reached a first threshold value;

in response to the determination that the read count for the first storage block has reached a first threshold value;

move the data in the first storage block to an available storage block of the plurality of storage blocks; and

back up the read counts for each storage block in the first zone to a non-volatile memory in the flash storage device;

determine that the read count of at least one of the storage blocks in a second zone of the plurality of zones has reached a second threshold value less than the first threshold value; and

back up the read counts for each storage block in the second zone to the non-volatile memory, in response to the determination that the read count of at least one of the storage blocks in the second zone has reached the second threshold value.

12. The flash storage device of claim 11, wherein the controller is further configured to maintain the read count for each of the plurality of storage blocks in the flash storage device containing data.

13. The flash storage device of claim 12, wherein maintaining the read count for each of the plurality of storage blocks containing data comprises storing the read counts in a random access memory in the flash storage device.

14. The flash storage device of claim 12, wherein the random access memory comprises a dynamic random access memory.

15. The flash storage device of claim 12, wherein maintaining the read count for each of the plurality of storage blocks containing data further comprises storing the read counts in the non-volatile memory in the flash storage device when the flash storage device is powered down.

16. The flash storage device of claim 12, wherein maintaining the read count for each of the plurality of storage blocks containing data further comprises storing the read counts in the non-volatile memory in the flash storage device at a predetermined interval.

17. The flash storage device of claim 11, wherein the controller is further configured to:

perform a read check on the requested data stored in the first storage block; and

move the data in the first storage block to an available storage block of the plurality of storage blocks when the read check fails.

18. The flash storage device of claim 17, wherein performing the read check comprises verifying the data stored in the first storage block using an error-correcting code in the stored data, and wherein the read check fails when an error count in the read-checked data is greater than a safety count.