Wear leveling method and controller using the same

• US 8,103,820 B2
• Filed: 03/12/2008
• Issued: 01/24/2012
• Est. Priority Date: 12/31/2007
• Status: Active Grant

• Current Assignee: Emtops Electronics Corp. (Phison Electronics Corporation)
• Original Assignee: Phison Electronics Corporation
• Inventors: Yeh, Chih-Kang, Chu, Chien-Hua
• Primary Examiner(s): RUTZ, JARED IAN
• Application Number:
  US12/047,127
• Publication Number:
  US 20090172255A1
• Time in Patent Office: 1,413 Days
• Field of Search: 711/103
• US Class Current: 711/103
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/7211 Wear leveling

Abstract

A wear leveling method for a multi level cell (MLC) NAND flash memory is provided. The flash memory includes a first zone and a second zone respectively having a plurality of blocks, wherein each of the blocks includes an upper page and a lower page. The wear leveling method includes: respectively determining whether to start a block swapping operation of a wear leveling process in the first zone and the second zone of the flash memory according to different start-up conditions; and respectively performing the block swapping operation in the first zone and the second zone, wherein the blocks in the first zone are accessed by using only the lower pages, and the blocks in the second zone are accessed by using both the upper pages and the lower pages. Thereby, the lifespan of the flash memory is effectively prolonged and meaningless consumption of system resources is avoided.

Claims

1. A wear leveling method, for a multi level cell (MLC) NAND flash memory, wherein the MLC NAND flash memory comprises a first zone having a plurality of blocks and a second zone having a plurality of blocks, and each of the blocks in the first zone and the second zone comprises an upper page and a lower page, the wear leveling method comprising:

determining whether to start a block swapping operation of a wear leveling process in the first zone of the MLC NAND flash memory according to a first start-up condition;

determining whether to start the block swapping operation in the second zone of the MLC NAND flash memory according to a second start-up condition, wherein the first start-up condition is different from the second start-up condition;

when the first start-up condition is met, performing the block swapping operation in the first zone; and

when the second start-up condition is met, performing the block swapping operation in the second zone,

wherein the blocks in the first zone are accessed by using only the lower pages, and the blocks in the second zone are accessed by using both the lower pages and the upper pages.

2. The wear leveling method according to claim 1, wherein the first start-up condition is that a first erased number of the first zone is greater than a first threshold, and the second start-up condition is that a second erased number of the second zone is greater than a second threshold,

wherein the first threshold is greater than the second threshold, and the corresponding first erased number or second erased number is reset after the block swapping operation is performed.

3. The wear leveling method according to claim 2, wherein when the first start-up condition is met, the block swapping operation is started in the first zone only when it is determined that a write command of a host is a non-continuous write command or a value gotten by subtracting the first threshold from the first erased number is greater than a predetermined upper limit;

and

wherein when the second start-up condition is met, the block swapping operation is started in the second zone only when it is determined that the write command of the host is a non-continuous write command or a value gotten by subtracting the second threshold from the second erased number is greater than the predetermined upper limit.

4. The wear leveling method according to claim 3, wherein when the first start-up condition and the second start-up condition are both met, the block swapping operation is started earlier in the second zone than the block swapping operation is done in the first zone.

5. The wear leveling method according to claim 3, wherein the block swapping operation is to move a block linked to a data area of the MLC NAND flash memory to a spare area of the MLC NAND flash memory, move a block linked to the spare area to the data area, and copy data in the block in the data area to the block in the spare area.

6. A wear leveling method, for a MLC NAND flash memory, wherein the MLC NAND flash memory comprises a first zone having a plurality of blocks and a second zone having a plurality of blocks, and each of the blocks in the first zone and the second zone comprises an upper page and a lower page, the wear leveling method comprising:

respectively performing a first wear leveling process and a second wear leveling process in the first zone and the second zone,

wherein the first wear leveling process is different from the second wear leveling process,

wherein the blocks in the first zone are accessed by using only the lower pages, and the blocks in the second zone are accessed by using both the lower pages and the upper pages.

7. The wear leveling method according to claim 6, wherein the first wear leveling process comprises:

counting a first erased number of the first zone; and

moving a block in the first zone which is linked to a data area of the MLC NAND flash memory to a spare area of the MLC NAND flash memory, moving a block in the first zone which is linked to the spare area to the data area, and copying data in the block in the data area to the block in the spare area when the first erased number is greater than a first threshold.

8. The wear leveling method according to claim 6, wherein the second wear leveling process comprises:

counting an erased number of each of the blocks in the second zone;

counting a second erased number of the second zone; and

moving a block in the second zone which is linked to a data area of the MLC NAND flash memory and has a relatively small erased number to a spare area of the MLC NAND flash memory, moving the block in the second zone which is linked to the spare area and has a relatively large erased number to the data area, and copying data in the block in the data area which has the relatively small erased number to the block in the spare area which has the relatively large erased number when the second erased number is greater than a second threshold.

9. A wear levelling method, for a flash memory module having a first flash memory and a second flash memory, the wear levelling method comprising:

determining whether to start a block swapping operation of a wear leveling process in the first flash memory according to a first start-up condition;

determining whether to start the block swapping operation in the second flash memory according to a second start-up condition, wherein the first start-up condition is different from the second start-up condition;

when the first start-up condition is met, performing the block swapping operation in the first flash memory; and

when the second start-up condition is met, performing the block swapping operation in the second flash memory,

wherein the first flash memory is a single level cell (SLC) NAND flash memory, and the second flash memory is a MLC NAND flash memory.

10. The wear leveling method according to claim 9, wherein the first start-up condition is that a first erased number of the first flash memory is greater than a first threshold, and the second start-up condition is that a second erased number of the second flash memory is greater than a second threshold,

wherein the first threshold is greater than the second threshold, and the corresponding first erased number or second erased number is reset after the block swapping operation is performed.

11. The wear leveling method according to claim 10, wherein when the first start-up condition is met, the block swapping operation is started in the first flash memory only when it is determined that a write command of a host is a non-continuous command or a value gotten by subtracting the first threshold from the first erased number is greater than a predetermined upper limit;

and

when the second start-up condition is met, the block swapping operation is started in the second flash memory only when it is determined that the write command of the host is a non-continuous command or a value gotten by subtracting the second threshold from the second erased number is greater than the predetermined upper limit.

12. The wear leveling method according to claim 11, wherein when the first start-up condition and the second start-up condition are both met, the block swapping operation is started earlier in the second flash memory than the block swapping operation is done in the first flash memory.

13. The wear leveling method according to claim 11, wherein the block swapping operation is to move a block linked to a data area of the flash memory module to a spare area of the flash memory module, move a block linked to the spare area to the data area, and copy data in the block in the data area to the block in the spare area.

14. A wear levelling method, for a flash memory module having a first flash memory and a second flash memory, the wear levelling method comprising:

respectively executing a first wear leveling process and a second wear leveling process in the first flash memory and the second flash memory of the flash memory module,

wherein the first wear leveling process is different from the second wear leveling process,

wherein the first flash memory is a SLC NAND flash memory, and the second flash memory is a MLC NAND flash memory.

15. The wear leveling method according to claim 14, wherein the first wear leveling process comprises:

counting a first erased number of the first flash memory; and

moving a block in the first flash memory which is linked to a data area of the first flash memory to a spare area of the first flash memory, moving a block in the first flash memory which is linked to the spare area to the data area, and copying data in the block in the data area to the block in the spare area when the first erased number is greater than a first threshold.

16. The wear leveling method according to claim 14, wherein the second wear leveling process comprises:

counting an erased number of each of the blocks in the second flash memory;

counting a second erased number of the second flash memory; and

moving a block in the second flash memory which is linked to a data area of the second flash memory and has a relatively small erased number to a spare area of the second flash memory, moving a block in the second flash memory which is linked to the spare area and has a relatively large erased number to the data area, and copying data in the block in the data area which has the relatively small erased number to the block in the spare area which has the relatively large erased number when the second erased number is greater than a second threshold.

17. A controller, for a MLC NAND flash memory in a storage apparatus, wherein the MLC NAND flash memory comprises a first zone having a plurality of blocks and a second zone having a plurality of blocks, and each of the blocks in the first zone and the second zone comprises an upper page and a lower page, the controller comprising:

a micro-processing unit;

a flash memory interface, electrically connected the micro-processing unit for accessing the MLC NAND flash memory;

a buffer memory, electrically connected the micro-processing unit for temporarily storing data; and

a memory management module, electrically connected the micro-processing unit for determining whether to start a block swapping operation of a wear leveling process in the first zone of the MLC NAND flash memory according to a first start-up condition and determining whether to start the block swapping operation in the second zone of the MLC NAND flash memory according to a second start-up condition, wherein the first start-up condition is different from the second start-up condition,

wherein when the first start-up condition is met, the memory management module performs the block swapping operation in the first zone,

wherein when the second start-up condition is met, memory management module performs the block swapping operation in the second zone,

wherein the blocks in the first zone are accessed by using only the lower pages, and the blocks in the second zone are accessed by using both the lower pages and the upper pages.

18. The controller according to claim 17, wherein the first start-up condition is that a first erased number of the first zone is greater than a first threshold, and the second start-up condition is that a second erased number of the second zone is greater than a second threshold,

wherein the first threshold is greater than the second threshold, and the corresponding first erased number or second erased number is reset after the block swapping operation is performed.

19. The controller according to claim 18, wherein when the first start-up condition is met, the memory management module starts the block swapping operation in the first zone only when the memory management module determines that a write command of a host is a non-continuous command or a value gotten by subtracting the first threshold from the first erased number is greater than a predetermined upper limit and the start-up condition of the block swapping operation in the second zone is not met;

and

wherein when the second start-up condition is met, the memory management module starts the block swapping operation in the second zone only when the memory management module determines that the write command of the host is a non-continuous command or a value gotten by subtracting the second threshold from the second erased number is greater than the predetermined upper limit.

20. The controller according to claim 19, wherein when the first start-up condition and the second start-up condition are both met, the memory management module starts the block swapping operation earlier in the second zone than the memory management module starts the block swapping operation in the first zone.

21. The controller according to claim 19, wherein the memory management module performs the block swapping operation to move a block linked to a data area of the MLC NAND flash memory to a spare area of the MLC NAND flash memory, move a block in the spare area to the data area, and copy data in the block in the data area to the block in the spare area.

22. The controller according to claim 17, wherein the storage apparatus is a universal serial bus (USB) flash disk, a flash memory card, or a solid state drive (SSD).

23. A controller, for a MLC NAND flash memory in a storage apparatus, wherein the MLC NAND flash memory comprises a first zone having a plurality of blocks and a second zone having a plurality of blocks, and each of the blocks in the first zone and the second zone comprises an upper page and a lower page, the controller comprising:

a micro-processing unit;

a flash memory interface, electrically connected the micro-processing unit for accessing the MLC NAND flash memory;

a buffer memory, electrically connected the micro-processing unit for temporarily storing data; and

a memory management module, electrically connected the micro-processing unit for respectively executing a first wear leveling process and a second wear leveling process in the first zone and the second zone,

wherein the first wear leveling process is different from the second wear leveling process,

wherein the blocks in the first zone are accessed by using only the lower pages, and the blocks in the second zone are accessed by using both the lower pages and the upper pages.

24. The controller according to claim 23, wherein the memory management module executes the first wear leveling process to count a first erased number of the first zone,

wherein when the first erased number is greater than a first threshold, a block in the first zone which is linked to a data area of the MLC NAND flash memory is moved to a spare area of the MLC NAND flash memory, a block in the first zone which is linked to the spare area is moved to the data area, and data in the block in the data area is copied to the block in the spare area.

25. The controller according to claim 23, wherein the memory management module executes the second wear leveling process to count an erased number of each of the blocks in the second zone and a second erased number of the second zone,

wherein when the second erased number is greater than a second threshold, a block in the second zone which is linked to the data area of the MLC NAND flash memory and has a relatively small erased number is moved to the spare area of the MLC NAND flash memory, a block in the second zone which is linked to the spare area and has a relatively large erased number is moved to the data area, and data in the block in the data area which has the relatively small erased number is copied to the block in the spare area which has the relatively large erased number.

26. The controller according to claim 23, wherein the storage apparatus is a USB flash disk, a flash memory card, or a SSD.

27. A controller, for a flash memory module in a storage apparatus, wherein the flash memory module comprises a first flash memory and a second flash memory, the controller comprising:

a micro-processing unit;

a flash memory interface, electrically connected the micro-processing unit for accessing the flash memory module;

a buffer memory, electrically connected the micro-processing unit for temporarily storing data; and

a memory management module, electrically connected the micro-processing unit for determining whether to start a block swapping operation of a wear leveling process in the first flash memory according to a first start-up condition and determining whether to start the block swapping operation in the second flash memory of the flash memory module according to a second start-up condition, wherein the first start-up condition is different from the second start-up condition,

wherein when the first start-up condition is met, the memory management module performs the block swapping operation in the first flash memory,

wherein when the second start-up condition is met, the memory management module performs the block swapping operation in the second flash memory,

wherein the first flash memory is a SLC NAND flash memory, and the second flash memory is a MLC NAND flash memory.

28. The controller according to claim 27, wherein the first start-up condition is that a first erased number of the first flash memory is greater than a first threshold, and the second start-up condition is that a second erased number of the second flash memory is greater than a second threshold,

wherein the first threshold is greater than the second threshold, and the memory management module resets the corresponding first erased number or second erased number after performing the block swapping operation.

29. The controller according to claim 28, wherein when the first start-up condition is met, the memory management module starts the block swapping operation in the first flash memory only when the memory management module determines that a write command of a host is a non-continuous command or a value gotten by subtracting the first threshold from the first erased number is greater than a predetermined upper limit and the start-up condition of the block swapping operation in the second flash memory is not met;

and

wherein when the second start-up condition is met, the memory management module starts the block swapping operation in the second flash memory only when the memory management module determines that the write command of the host is a non-continuous command or a value gotten by subtracting the second threshold from the second erased number is greater than the predetermined upper limit.

30. The controller according to claim 29, wherein when the first start-up condition and the second start-up condition are both met, the memory management module starts the block swapping operation earlier in the second flash memory than the memory management module starts the block swapping operation in the first flash memory.

31. The controller according to claim 27, wherein the storage apparatus is a USB flash disk, a flash memory card, or a SSD.

32. A controller, for a flash memory module in a storage apparatus, wherein the flash memory module comprises a first flash memory and a second flash memory, the controller comprising:

a micro-processing unit;

a flash memory interface, electrically connected the micro-processing unit for accessing the flash memory module;

a buffer memory, electrically connected the micro-processing unit for temporarily storing data; and

a memory management module, electrically connected the micro-processing unit for respectively executing a first wear leveling process and a second wear leveling process in the first flash memory and the second flash memory of the flash memory module,

wherein the first wear leveling process is different from the second wear leveling process,

wherein the first flash memory is a SLC NAND flash memory, and the second flash memory is a MLC NAND flash memory.

33. The controller according to claim 32, wherein the memory management module executes the first wear leveling process to count a first erased number of the first flash memory,

wherein when the first erased number is greater than a first threshold, a block in the first flash memory which is linked to a data area of the first flash memory is moved to a spare area of the first flash memory, a block in the first flash memory which is linked to the spare area is moved to the data area, and data in the block in the data area is copied to the block in the spare area.

34. The controller according to claim 32, wherein the memory management module executes the second wear leveling process to count an erased number of each of the blocks in the second flash memory and a second erased number of the second flash memory,

wherein when the second erased number is greater than a second threshold, a block in the second flash memory which is linked to a data area of the second flash memory and has a relatively small erased number is moved to a spare area of the second flash memory, a block in the second flash memory which is linked to the spare area and has a relatively large erased number is moved to the data area, and data in the block in the data area which has the relative low erased number is copied to the block in the spare area which has the relatively large erased number.

35. The controller according to claim 32, wherein the storage apparatus is a USB flash disk, a flash memory card, or a SSD.