WEAR LEVELING METHOD, AND STORAGE SYSTEM AND CONTROLLER USING THE SAME

• US 20100023675A1
• Filed: 11/06/2008
• Published: 01/28/2010
• Est. Priority Date: 07/23/2008
• Status: Active Grant

• Current Assignee: Phison Electronics Corporation
• Original Assignee: Phison Electronics Corporation
• Inventors: CHEN, RUEI-CIAN, Yeh, Chih-Kang, Seng, Kian-Fui
• Granted Patent: US 8,086,787 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 2212/7211 Wear leveling

Abstract

A wear leveling method for a flash is provided, wherein the flash memory includes a plurality of physical blocks grouped into at least a data area and a spare area. The method includes setting a first predetermined threshold value as a wear-leveling start value and randomly generating a random number as a memory erased count, wherein the random number is smaller than the wear-leveling start value. The method also includes counting the memory erased count each time when the physical blocks are erased and determining whether the memory erased count is smaller than the wear-leveling start value, wherein a physical blocks switching is performed between the data area and the spare area when the memory erased count is not smaller then the wear-leveling start value. Accordingly, it is possible to uniformly use the physical blocks, so as to effectively prolong a lifetime of the store system.

Claims

1. A wear leveling method, adapted to a flash memory of a storage system, wherein the flash memory comprises a plurality of physical blocks grouped into at least a data area and a spare area, the wear leveling method comprising:

setting a first predetermined threshold value as a wear-leveling start value;

randomly generating a random number as a memory erased count, wherein the random number is less than the wear-leveling start value;

counting the memory erased count each time when the physical blocks are erased; and

determining whether the memory erased count is less than the wear-leveling start value, wherein a physical blocks switching is performed between the data area and the spare area when the memory erased count is not less then the wear-leveling start value.

2. The wear leveling method as claimed in claim 1, wherein the step of performing the physical blocks switching between the data area and the spare area includes:

respectively selecting a physical block from the data area and the spare area;

copying data on the physical block selected from the data area to the physical block selected from the spare area;

associating the physical block selected from the data area with the spare area; and

associating the physical block selected from the spare area with the data area.

3. The wear leveling method as claimed in claim 2, further comprising:

recording an erased count of each of the physical blocks; and

counting the erased count of the erased physical block each time when the physical blocks are erased.

4. The wear leveling method as claimed in claim 3 wherein the step of respectively selecting a physical block from the data area and the spare area includes:

selecting a physical block having a minimum erase times from the data area; and

selecting a physical block having a maximum erase times from the spare area.

5. The wear leveling method as claimed in claim 2, wherein the step of respectively selecting a physical block from the data area and the spare area includes sequentially or randomly selecting a physical block from the data area and the spare area, respectively.

6. The wear leveling method as claimed in claim 3, further comprising:

calculating an average erased count according to the erased counts of the physical blocks;

judging whether the average erased count is greater than a wearing threshold value; and

replacing the first predetermined threshold value by a second predetermined threshold value to serve as the wear-leveling start value when the average erased count is grater than the wearing threshold value, wherein the second predetermined threshold value is less than the first predetermined threshold value.

7. The wear leveling method as claimed in claim 3 further comprising adjusting the erased counts of the physical blocks of the spare area when the storage system is booted.

8. The wear leveling method as claimed in claim 1, wherein the step of randomly generating the random number as the memory erased count is executed while the storage system is booted.

9. The wear leveling method as claimed in claim 3, further comprising:

judging whether the erased count of each of the physical blocks is greater than the wearing threshold value; and

replacing the first predetermined threshold value by a second predetermined threshold value to serve as the wear-leveling start value when at least one of the erased count of the physical blocks is grater than the wearing threshold value, wherein the second predetermined threshold value is less than the first predetermined threshold value.

10. The wear leveling method as claimed in claim 7, wherein the step of adjusting the erased count of the physical block of the spare area includes adding the erased count of the physical block of the spare area by an adjusting number.

11. A controller, adapted to a storage system having a flash memory, wherein the flash memory comprises a plurality of physical blocks grouped into at least a data area and a spare area, the controller comprising:

a micro-processing unit;

a flash memory interface module, coupled to the micro-processing unit;

a host interface module, coupled to the micro-processing unit;

a buffer memory, coupled to the micro-processing unit; and

a memory management module, coupled to the micro-processing unit, and having a plurality of machine commands that can be executed by the micro-processing unit for executing a plurality of wear leveling steps to the flash memory, the wear leveling steps comprise;

setting a first predetermined threshold value as a wear-leveling start value;

randomly generating a random number as a memory erased count, wherein the random number is less than the wear-leveling start value;

counting the memory erased count each time when the physical blocks are erased; and

determining whether the memory erased count is less than the wear-leveling start value, wherein a physical blocks switching is performed between the data area and the spare area when the memory erased count is not less then the wear-leveling start value.

12. The controller as claimed in claim 11, wherein the step of performing the physical blocks switching between the data area and the spare area includes:

respectively selecting a physical block from the data area and the spare area;

copying data on the physical block selected from the data area to the physical block selected from the spare area;

associating the physical block selected from the data area to the spare area; and

associating the physical block selected from the spare area to the data area.

13. The controller as claimed in claim 12, wherein the wear leveling steps further comprise:

recording an erased count of each of the physical blocks; and

counting the erased count of the erased physical block each time when the physical blocks are erased.

14. The controller as claimed in claim 13, wherein the step of respectively selecting a physical block from the data area and the spare area includes:

selecting a physical block having a minimum erase times from the data area; and

selecting a physical block having a maximum erase times from the spare area.

15. The controller as claimed in claim 12, wherein the step of respectively selecting a physical block from the data area and the spare area includes sequentially or randomly selecting a physical block from the data area and the spare area, respectively.

16. The controller as claimed in claim 13, wherein the wear leveling steps further comprise:

calculating an average erased count according to the erased counts of the physical blocks;

judging whether the average erased count is greater than a wearing threshold value; and

replacing the first predetermined threshold value by a second predetermined threshold value to serve as the wear-leveling start value when the average erased count is grater than the wearing threshold value, wherein the second predetermined threshold value is less than the first predetermined threshold value.

17. The controller as claimed in claim 13, wherein the step of adjusting the erased count of the physical block of the spare area includes adding the erased count of the physical block of the spare area by an adjusting number.

18. A storage system, comprising:

a flash memory, having a plurality of physical blocks grouped into at least a data area and a spare area;

a connector; and

a controller, electrically connected to the flash memory and the connector, the controller executing a plurality of machine commands of a memory management module to execute a plurality of wear leveling steps, and the wear leveling steps comprising;

setting a first predetermined threshold value as a wear-leveling start value;

randomly generating a random number as a memory erased count, wherein the random number is less than the wear-leveling start value;

counting the memory erased count each time when the physical blocks are erased; and

determining whether the memory erased count is less than the wear-leveling start value, wherein a physical blocks switching is performed between the data area and the spare area when the memory erased count is not less then the wear-leveling start value.

19. The storage system as claimed in claim 18, wherein the step of performing the physical blocks switching between the data area and the spare area includes:

respectively selecting a physical block from the data area and the spare area;

copying data on the physical block selected from the data area to the physical block selected from the spare area;

associating the physical block selected from the data area to the spare area; and

associating the physical block selected from the spare area to the data area.

20. The storage system as claimed in claim 19, wherein the wear leveling steps further comprise:

recording an erased count of each of the physical blocks; and

counting the erased count of the erased physical block each time when the physical blocks are erased.