SLC-MLC Wear Balancing

• US 20130173844A1
• Filed: 12/29/2011
• Published: 07/04/2013
• Est. Priority Date: 12/29/2011
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Chen, Jian, Gorobets, Sergey Anatolievich, Sprouse, Steven
• Granted Patent: US 9,176,862 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 2212/7202 Allocation control and policies
• CPC Class Codes: G06F 2212/7211 Wear leveling
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles
• CPC Class Codes: G11C 2211/5641 Multilevel memory having cells with different number of storage levels

Abstract

A method and system for SLC-MLC Wear Balancing in a flash memory device is disclosed. The flash memory device includes a single level cell (SLC) portion and a multi-level cell (MLC) portion. The age of the SLC portion and the MLC portion may differ, leading potentially to one portion wearing out before the other. In order to avoid this, a controller is configured to receive an age indicator from one or both of the SLC portion and the MLC portion, determine, based on the age indicator, whether to modify operation of the SLC portion and/or the MLC portion, and in response to determining to modifying operation, modify the operation of the at least one of the SLC portion or the MLC portion. The modification of the operation may thus balance wear between the SLC and MLC portions, thereby potentially extending the life of the flash memory device.

Claims

1. A method for managing usage of a single level cell (SLC) portion and a multi-level cell (MLC) portion in a flash storage device, the method comprising:

in the flash storage device having a controller and a memory in communication with the controller, the memory including the SLC portion and the MLC portion;

accessing an age indicator for the flash storage device;

determining, based on the age indicator, whether to modify operation of at least one of the SLC portion or the MLC portion; and

in response to determining to modify operation of at least one of the SLC portion or the MLC portion, modifying the operation of the at least one of the SLC portion or the MLC portion.

2. The method of claim 1, wherein the age indicator for the flash storage device comprises an age indicator for part or all of the SLC portion or the MLC portion.

3. The method of claim 1, wherein accessing the age indicator for the flash storage device comprises:

accessing an SLC age indicator indicative of age of at least a part of the SLC portion; and

accessing an MLC age indicator indicative of age of at least a part of the MLC portion;

wherein determining whether to modify the operation of at least one of the SLC portion or the MLC portion is based on both the SLC age indicator and the MLC age indicator.

4. The method of claim 1, wherein the age indicator comprises one or more of:

P/E block counts, individual or average per partition (logical or SLC/MLC);

number of total blocks left;

number of spares left/number of blocks failed;

ECC based bit error rate (BER);

program/erase time;

CVD, state shift level.

5. The method of claim 1, wherein determining, based on the age indicator, whether to modify operation of at least one of the SLC portion or the MLC portion comprises:

comparing the age indicator with a data construct indicative of preferred SLC wear to MLC wear; and

determining to modify the operation based on the comparison.

6. The method of claim 5, wherein the data construct indicative of the preferred SLC wear to MLC wear comprises data indicative of wear so that the SLC portion and the MLC portion reach a maximum number of P/E cycles at end of life of the flash storage device.

7. The method of claim 1, wherein the operation of the at least one of the SLC portion or the MLC portion is based on a parameter;

and

wherein modifying the operation of the at least one of the SLC portion or the MLC portion comprises changing a value of the parameter.

8. The method of claim 7, wherein the parameter comprises a threshold for cold data eviction from the SLC portion to the MLC portion.

9. The method of claim 7, wherein the parameter comprises one or more thresholds for determining whether to write host data into the MLC portion or the SLC portion.

10. The method of claim 1, wherein the operation of the at least one of the SLC portion or the MLC portion is based on multiple parameters;

and

further comprising determining one or more of the multiple parameters to modify; and

wherein modifying the operation of the at least one of the SLC portion or the MLC portion comprises modifying the determined one or more multiple parameters.

11. The method of claim 10, wherein the age indicator for the flash storage device comprises an age indicator for part or all of the SLC portion or the MLC portion;

and

wherein determining the one or more of the multiple parameters to modify is based on the SLC age indicator and the MLC age indicator.

12. The method of claim 10, further comprising selecting one or more values for the determining one or more multiple parameters;

and

wherein modifying the determined one or more multiple parameters comprises using the selected one or more values to modify the determined one or more multiple parameters.

13. A storage device comprising:

a memory including an single level cell (SLC) portion and a multi-level cell (MLC) portion; and

a controller in communication with the memory, the controller configured to;

access an age indicator for the flash storage device;

determine, based on the age indicator, whether to modify operation of at least one of the SLC portion or the MLC portion; and

in response to determining to modify operation of at least one of the SLC portion or the MLC portion, modify the operation of the at least one of the SLC portion or the MLC portion.

14. The storage device of claim 13, wherein the age indicator for the flash storage device comprises an age indicator for part or all of the SLC portion or the MLC portion.

15. The storage device of claim 13, wherein the controller is configured to access the age indicator for the flash storage device by:

accessing an SLC age indicator indicative of age of at least a part of the SLC portion; and

accessing an MLC age indicator indicative of age of at least a part of the MLC portion;

wherein the controller is configured to determine whether to modify the operation of at least one of the SLC portion or the MLC portion based on both the SLC age indicator and the MLC age indicator.

16. The storage device of claim 13, wherein the age indicator comprises one or more of:

P/E block counts, individual or average per partition (logical or SLC/MLC);

number of total blocks left;

number of spares left/number of blocks failed;

ECC based bit error rate (BER);

program/erase time;

CVD, state shift level.

17. The storage device of claim 13, wherein the controller is configured to determine, based on the age indicator, whether to modify operation of at least one of the SLC portion or the MLC portion by:

comparing the age indicator with a data construct indicative of preferred SLC wear to MLC wear; and

determining to modify the operation based on the comparison.

18. The storage device of claim 17, wherein the data construct indicative of the preferred SLC wear to MLC wear comprises data indicative of wear so that the SLC portion and the MLC portion reach a maximum number of P/E cycles at end of life of the storage device.

19. The storage device of claim 13, wherein the operation of the at least one of the SLC portion or the MLC portion is based on a parameter;

and

wherein the controller is configured to modify the operation of the at least one of the SLC portion or the MLC portion by changing a value of the parameter.

20. The storage device of claim 19, wherein the parameter comprises a threshold for cold data eviction from the SLC portion to the MLC portion.

21. The storage device of claim 19, wherein the parameter comprises one or more thresholds for determining whether to write host data into the MLC portion or the SLC portion.

22. The storage device of claim 13, wherein the operation of the at least one of the SLC portion or the MLC portion is based on multiple parameters;

and

wherein the controller is further configured to determine one or more of the multiple parameters to modify; and

wherein the controller is configured to modify the operation of the at least one of the SLC portion or the MLC portion by modifying the determined one or more multiple parameters.

23. The storage device of claim 22, wherein the age indicator for the flash storage device comprises an age indicator for part or all of the SLC portion or the MLC portion;

and

wherein the controller is configured to determine the one or more of the multiple parameters to modify based on the SLC age indicator and the MLC age indicator.

24. The storage device of claim 22, wherein the controller is further configured to select one or more values for the determining one or more multiple parameters;

and

wherein the controller is configured to modify the determined one or more multiple parameters comprises using the selected one or more values to modify the determined one or more multiple parameters.