SLC-MLC wear balancing

• US 9,176,862 B2
• Filed: 12/29/2011
• Issued: 11/03/2015
• 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
• Primary Examiner(s): Thai, Tuan
• Assistant Examiner(s): Waddy, Jr., Edward
• Application Number:
  US13/340,446
• Publication Number:
  US 20130173844A1
• Time in Patent Office: 1,405 Days
• Field of Search: 711/103, 711/E12.008, 711/E12.001, 711/156, 711/154, 711/167, 711/E12.078, 711/E12.103, 711/151
• US Class Current: 1/1
• 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 storage device, the method comprising:

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

accessing a current SLC-MLC wear balance for the storage device;

determining, based on the current SLC-MLC wear balance, whether to change a value of a parameter, the value of the parameter used to determine whether to perform an operation on at least one of the SLC portion or the MLC portion;

in response to determining to change the value of the parameter, selecting a new value for the parameter, the new value being different from the value of the parameter and being selected based on the current SLC-MLC wear balance for the storage device;

changing the value of the parameter to the new value; and

after changing the value of the parameter, using the new value of the parameter to determine whether to perform the operation on the at least one of the SLC portion or the MLC portion.

2. The method of claim 1, wherein the storage device comprises a flash storage device;

further comprising;

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

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

determining the current SLC-MLC wear balance based on the current SLC age indicator and the current MLC age indicator.

3. The method of claim 1, wherein the parameter comprises a threshold for cold data eviction from the SLC portion to the MLC portion.

4. The method of claim 1, wherein the operation comprises determining whether to perform an action in the SLC portion or in the MLC portion;

wherein determining whether to perform the action in the SLC portion or in the MLC portion is dependent on the value of the parameter; and

wherein changing the value of the parameter changes the determination whether to perform the action in the SLC portion or in the MLC portion.

5. The method of claim 4, wherein the action comprises writing host data;

wherein determining whether to write the host data into the SLC portion or the MLC portion is dependent on the value of the parameter; and

wherein changing the value of the parameter changes the determination whether the host data is written into the SLC portion or into the MLC portion.

6. The method of claim 1, wherein the operation comprises determining where, within the SLC portion, to write host data;

wherein determining where, within the SLC portion, to write the host data is dependent on the value of the parameter; and

wherein changing the value of the parameter changes the determination where, within the SLC portion, to write the host data.

7. The method of claim 6, wherein the SLC portion comprises a binary cache and one or more update blocks;

and

wherein changing the value of the parameter changes the determination whether to store the host data in the binary cache or in the one or more update blocks.

8. The method of claim 1, wherein the operation comprises folding data from the SLC portion to the MLC portion;

wherein determining whether to fold the data from the SLC portion to the MLC portion is dependent on the value of the parameter; and

wherein, in response to determining to reduce wear on the SLC portion, the parameter is changed in order to fold the data from the SLC portion to the MLC portion earlier.

9. The method of claim 1, wherein the operation comprises evicting cold data from the SLC portion to the MLC portion;

wherein determining whether to evict the cold data from the SLC portion to the MLC portion is dependent on the value of the parameter;

wherein, in response to determining to reduce wear on the SLC portion, the parameter is changed in order to evict more of the cold data from the SLC portion to the MLC portion sooner; and

wherein, in response to determining to reduce wear on the MLC portion, the parameter is changed in order to maintain more of the cold data in the SLC portion.

10. The method of claim 1, wherein the parameter has an associated plurality of potential modifications;

and

wherein selecting the new value for the parameter comprises selecting, based on the current SLC-MLC wear balance, one of the plurality of potential modifications.

11. The method of claim 1, wherein selecting the new value of the parameter is based on a deviation of the current SLC-MLC wear balance from a preferred SLC-MLC wear balance.

12. The method of claim 1, wherein determining, based on the current SLC-MLC wear balance, whether to change the value of the parameter comprises:

dynamically selecting which parameter, from a plurality of potential parameters, to change based on the current SLC-MLC wear balance.

13. A storage device comprising:

a memory including a 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 a current SLC-MLC wear balance for the storage device;

determine, based on the current SLC-MLC wear balance, whether to change a value of a parameter, the value of the parameter used to determine whether to perform an operation on at least one of the SLC portion or the MLC portion;

in response to determining to change the value of the parameter, select a new value for the parameter, the new value being different from the value of the parameter and being selected based on the current SLC-MLC wear balance for the storage device;

change the value of the parameter to the new value; and

after changing the value of the parameter, use the new value of the parameter to determine whether to perform the operation on the at least one of the SLC portion or the MLC portion.

14. The storage device of claim 13, wherein the storage device comprises a flash storage device;

wherein the controller is further configured to;

access a current SLC age indicator indicative of age of at least a part of the SLC portion;

access a current MLC age indicator indicative of age of at least a part of the MLC portion; and

determine the current SLC-MLC wear balance based on the current SLC age indicator and the current MLC age indicator.

15. The storage device of claim 13, wherein the parameter comprises a threshold for cold data eviction from the SLC portion to the MLC portion.

16. The storage device of claim 13, wherein the operation comprises determining whether to perform an action in the SLC portion or in the MLC portion;

wherein the controller is configured to determine whether to perform the action in the SLC portion or in the MLC portion based on the value of the parameter; and

wherein the controller is configured to change the value of the parameter in order to change the determination whether to perform the action in the SLC portion or in the MLC portion.

17. The storage device of claim 16, wherein the action comprises writing host data;

wherein the controller is configured to determine whether to write the host data into the SLC portion or the MLC portion based on the value of the parameter; and

wherein the controller is configured to change the value of the parameter in order to change the determination whether to write the host data into the SLC portion or into the MLC portion.

18. The storage device of claim 13, wherein the operation comprises determining where, within the SLC portion, to write host data;

wherein the controller is configured to determine where, within the SLC portion, to write the host data is dependent on the value of the parameter; and

wherein the controller is configured to change the value of the parameter in order to change the determination where, within the SLC portion, to write the host data.

19. The storage device of claim 18, wherein the SLC portion comprises a binary cache and one or more update blocks;

and

wherein the controller is configured to change the value of the parameter in order to change the determination whether to store the host data in the binary cache or in the one or more update blocks.

20. The storage device of claim 13, wherein the operation comprises folding data from the SLC portion to the MLC portion;

wherein the controller is configured to determine whether to fold the data from the SLC portion to the MLC portion based on the value of the parameter; and

wherein, in response to determining to reduce wear on the SLC portion, the controller is configured to change the parameter in order to fold the data from the SLC portion to the MLC portion earlier.

21. The storage device of claim 13, wherein the operation comprises evicting cold data from the SLC portion to the MLC portion;

wherein the controller is configured to determine whether to evict the cold data from the SLC portion to the MLC portion based on the value of the parameter;

wherein, in response to determining to reduce wear on the SLC portion, the controller is configured to change the parameter in order to evict more of the cold data from the SLC portion to the MLC portion sooner; and

wherein, in response to determining to reduce wear on the MLC portion, the controller is configured to change the parameter in order to maintain more of the cold data in the SLC portion.

22. The storage device of claim 13, wherein the parameter has an associated plurality of potential modifications;

and

wherein the controller is configured to select the new value for the parameter by selecting, based on the current SLC-MLC wear balance, one of the plurality of potential modifications.

23. The storage device of claim 13, wherein the controller is configured to select the new value of the parameter based on a deviation of the current SLC-MLC wear balance from a preferred SLC-MLC wear balance.