Adaptive storage reliability management

• US 9,952,781 B2
• Filed: 11/03/2014
• Issued: 04/24/2018
• Est. Priority Date: 10/20/2014
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Inventors: Orme, Evan, Peterson, James G.
• Primary Examiner(s): Mercado, Ramon A.
• Application Number:
  US14/531,891
• Publication Number:
  US 20160110249A1
• Time in Patent Office: 1,268 Days
• CPC Class Codes: G06F 11/1016 Error in accessing a memory location, i.e. addressing error
• CPC Class Codes: G06F 11/1044 with specific ECC/EDC distribution
• CPC Class Codes: G06F 11/1048 using arrangements adapted for a specific error detection or correction feature
• CPC Class Codes: G06F 11/1072 in multilevel memories
• CPC Class Codes: G06F 12/0238 Memory management in non-volatile memory, e.g. resistive RAM or ferroelectric memory
• CPC Class Codes: G06F 2212/1032 Reliability improvement, data loss prevention, degraded operation etc
• CPC Class Codes: G06F 2212/152 Virtualized environment, e.g. logically partitioned system
• CPC Class Codes: G06F 2212/202 Non-volatile memory
• CPC Class Codes: G06F 2212/214 Solid state disk
• CPC Class Codes: G06F 2212/7205 Cleaning, compaction, garbage collection, erase control
• CPC Class Codes: G11C 16/16 for erasing blocks, e.g. arrays, words, groups
• CPC Class Codes: G11C 2029/0409 Online test
• CPC Class Codes: G11C 29/52 Protection of memory contents; Detection of errors in memory contents

Abstract

A storage controller identifies a storage location within a storage division that corresponds to a high error rate. In response, the storage controller may refresh data stored on the storage division by relocating data from the storage division and/or initializing (e.g., erasing) the storage division. In some embodiments, the storage division is selectively refreshed by relocating data from the storage location(s) having high error rates, while deferring a full relocation of other data from the storage division. The storage division may be selectively refreshed based on reliability characteristics of the storage division, such as the remaining data retention time calculated for the storage division.

Claims

1. A method, comprising:

determining a reliability metric of a first storage unit within a first erase division of a non-volatile memory comprising a plurality of erase divisions, each erase division having a plurality of storage units;

determining a remaining retention time for the first erase division based on one or more reliability metrics of one or more storage units of the first erase division, the one or more storage units of the first erase division excluding the first storage unit; and

performing a partial refresh operation of the first erase division in response to the determined reliability metric of the first storage unit and the remaining retention time of the first erase division, the partial refresh operation comprising;

relocating data stored on the first storage unit from the first erase division to another one of the erase divisions, and

deferring relocation of data stored on the one or more storage units from the first erase division based on the determined remaining retention time.

2. The method of claim 1, further comprising correcting read errors in the data stored on the first storage unit by use of an error-correcting code.

3. The method of claim 1, wherein relocating the data stored on the first storage unit comprises:

identifying data for relocation from the first erase division based on reliability metrics of the respective storage units of the first erase division; and

selectively relocating the identified data to one or more other erase divisions.

4. The method of claim 1, wherein determining the remaining retention time for the erase division comprises determining a reliability metric for a second storage unit of the first erase division.

5. The method of claim 1, wherein the one or more storage units include storage units of the first erase division determined to comprise valid data and exclude storage units of the first erase division determined to comprise invalid data.

6. The method of claim 1, wherein determining the remaining retention time of the first erase division comprises determining a current error rate of the first erase division based on error rates corresponding to read operations performed on the one or more storage units.

7. The method of claim 1, further comprising:

identifying storage units within the first erase division that are in use to store valid data, wherein the one or more storage units comprise the identified storage units.

8. The method of claim 1, wherein the one or more storage units are identified in response to determining that the one or more storage units are associated with logical addresses in a forward map.

9. The method of claim 8, wherein the one or more storage units exclude storage units of the first erase division that are not associated with logical addresses in the forward map.

10. The method of claim 1, wherein the first erase division comprises one of an erase block, a group of erase blocks, and a logical erase block.

11. The method of claim 1, wherein deferring relocation of data stored on the one or more storage units from the first erase division comprises postponing a garbage collection operation on the first erase division, the garbage collection operation comprising:

identifying valid data stored on the first erase division;

relocating the valid data stored on the first erase division to another erase division; and

initializing the first erase division.

12. An apparatus, comprising:

a reliability monitor configured to identify a first physical address within a first storage division of a storage medium having a plurality of storage divisions each comprising a plurality of physical addresses, the identified first physical address corresponding to an error rate that exceeds an error rate threshold; and

a reliability manager, wherein in response to identifying the first physical address, the reliability manager is configured to;

determine a reliability metric corresponding to one or more physical addresses of the first storage division other than the identified first physical address,

write data stored at the identified first physical address from the first storage division to a different physical address of another one of the storage divisions of the storage medium, and

retain data stored at the one or more physical addresses of the first storage division based on the determined reliability metric.

13. The apparatus of claim 12, further comprising:

a translation layer configured to associate logical identifiers of a logical address space with respective physical addresses of the storage medium,

wherein the reliability manager is configured to remap a logical identifier from the identified first physical address to the different physical address by use of the translation layer, and

wherein the one or more physical addresses comprise physical addresses of the first storage division that are associated with logical identifiers of the logical address space by the translation layer.

14. The apparatus of claim 12, wherein the reliability manager is configured to:

determine a remaining retention time for the first storage division based on the reliability metric; and

relocate data from the first storage division after the determined retention time.

15. The apparatus of claim 12, wherein the reliability manager determines the reliability metric based on one or more of an error rate of the one or more physical addresses, a reliability projection for the first storage division, a reliability model for the first storage division, a partial reliability metric of the first storage division, an error rate projection, and a data retention guarantee.

16. The apparatus of claim 12, wherein the reliability metric is based on test read operations performed on the one or more physical addresses of the first storage division.

17. The apparatus of claim 12, wherein the reliability manager identifies the first physical address corresponding to the error rate that exceeds the error rate threshold in response to one or more of servicing a request to read data from the first physical address, and a reliability scan.

18. A system, comprising:

a flash storage medium comprising a plurality of erase blocks, each erase block comprising a plurality of pages;

means for identifying a page of a particular erase block having a bit error rate that exceeds a threshold;

means for determining a remaining data retention time for data stored on one or more pages of the particular erase block other than the identified page; and

means for selectively refreshing the particular erase block in response to the identified page having a bit error rate that exceeds the threshold and the determined remaining data retention time not exceeding a duration threshold, by;

writing data stored on the identified page to a page on a different erase block of the flash storage medium, and

retaining data stored on the one or more pages on the particular erase block for the determined remaining data retention time.

19. The system of claim 18, wherein the determined remaining data retention time of the particular erase block is based on one or more of:

time elapsed since the particular erase block was programmed,

bit error rates of the one or more pages of the particular erase block,

a bit error rate projection for the one or more pages of the particular erase block,

a bit error rate model for the one or more pages of the particular erase block, and

a data retention guarantee pertaining to data stored on the flash storage medium.