Method for non-volatile memory with worst-case control data management

• US 20080091901A1
• Filed: 10/12/2006
• Published: 04/17/2008
• Est. Priority Date: 10/12/2006
• Status: Abandoned Application

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Inventors: Bennett, Alan David, Gorobets, Sergey Anatolievich, Hutchison, Neil David
• Application Number:
  US11/549,035
• Publication Number:
  US 20080091901A1
• Time in Patent Office: Days
• US Class Current: 711/165
• 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 2212/7205 Cleaning, compaction, garbage collection, erase control

Abstract

In a nonvolatile memory with a block management system, data written to blocks include host write data and also system control data for managing the blocks. When a block is full or no longer accepting data, it is closed after valid versions of the data on it are relocated to another block in a rewrite operation. An improved pre-emptive rewrite scheme prevents a worst-case situation where multiple rewrites to occur at once when they happened to be full at the same time. Particularly, the scheduling of the pre-emptive rewrites for control data is based on a number of considerations including the time required for each control block rewrite and the time available for control block rewrites based on the configuration of the update blocks for storing host data, the time required in the foreground host operation and the host write latency.

Claims

1. A method of operating a memory, comprising:

organizing a nonvolatile memory into blocks;

maintaining one or more type of data;

setting a margin of a number of empty memory units before a block is full for each type of data, wherein the margin is substantially sufficient to accommodate data accumulated in a predetermined interval before data in the block are allowed to relocate;

storing updates of the one or more type of data among a plurality of blocks so that each block is storing essentially data of the same type; and

in response to a block storing data reaching the margin for the data type, relocating data in the block to another block when allowed to do so.

2. The method as in claim 1, wherein:

operating the memory includes a host writing thereto, and

the predetermined interval is dependent on a worst-case host write pattern that yields a maximum interval before data in the block are allowed to relocate.

3. The method as in claim 1, wherein:

the predetermined interval is dependent on a worst-case configuration of blocks that yields a maximum amount of data to relocate.

4. The method as in claim 1, further comprising:

assigning a ranking to each type of data if more than one; and

wherein

said relocating data is responsive to a block storing data reaching the margin for the data type and having data type of a highest rank among any similar blocks.

5. The method as in claim 4, wherein the type of data having the highest rank is one that is expected to fill the blocks the fastest.

6. The method as in claim 1, wherein the different types of data are control data the memory uses to manage the blocks.

7. The method as in claim 6, wherein the different types of control data include one that controls provisioning of the blocks.

8. The method as in claim 6, wherein the different types of control data include one that pertains to location of data stored in the blocks.

9. The method as in claim 6, wherein data in the block are allowed to relocate during execution of a host command on the memory.

10. The method as in claim 1, wherein the determination of the predetermined interval before data in the block are allowed to relocate includes the time required for relocating the data in the block.

11. The method as in claim 1, wherein the determination of the predetermined interval before data in the block are allowed to relocate includes how a pool of blocks opened for receiving host data is configured.

12. The method as in claim 1, wherein the determination of the predetermined interval before data in the block are allowed to relocate includes a maximum time set by a host command.

13. The method as in claim 1, wherein the data in each block are erasable together.

14. The method as in claim 2, wherein the data in each block are erasable together.

15. The method as in claim 3, wherein the data in each block are erasable together.

16. The method as in claim 4, wherein the data in each block are erasable together.

17. The method as in claim 5, wherein the data in each block are erasable together.

18. The method as in claim 6, wherein the data in each block are erasable together.

19. The method as in claim 7, wherein the data in each block are erasable together.

20. The method as in claim 8, wherein the data in each block are erasable together.

21. The method as in claim 9, wherein the data in each block are erasable together.

22. The method as in claim 10, wherein the data in each block are erasable together.

23. The method as in claim 11, wherein the data in each block are erasable together.

24. The method as in claim 12, wherein the data in each block are erasable together.

25. The method as in claim 1, wherein the memory is a one-time programmable memory.

26. The method as in claim 1, wherein the memory is flash EEPROM.

27. The method as in claim 1, wherein the memory is embodied in a removable memory card.

28. The method as any one of claims 1 to 27, wherein the memory has memory cells that each stores one bit of data.

29. The method as any one of claims 1 to 27, wherein the memory has memory cells that each stores more than one bit of data.