Flash memory management method that is resistant to data corruption by power loss

• US 20060259718A1
• Filed: 03/09/2006
• Published: 11/16/2006
• Est. Priority Date: 05/12/2005
• Status: Active Grant

• Current Assignee: Western Digital Israel Limited (Western Digital Corporation)
• Original Assignee: M-Systems Flash Disk Pioneers Ltd. (Western Digital Corporation)
• Inventors: Paley, Alexander
• Granted Patent: US 7,275,140 B2
• Time in Patent Office: Days
• US Class Current: 711/159
• CPC Class Codes: G06F 11/1072 in multilevel memories
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/22 Safety or protection circuits preventing unauthorised or accidental access to memory cells

Abstract

A method of managing page-based data storage media such as flash media, a system that uses the method, and a computer-readable storage medium bearing code for implementing the method. For each page, a corresponding risk zone, of other pages whose data are put at risk of corruption if writing to the page is interrupted, is identified. When a page is selected for writing new data, the written pages in its risk zone are copied to a log. As necessary, corrupt data are replaced with corresponding data from the log.

Claims

1. A method of managing a memory that includes a plurality of pages, the method comprising the steps of:

(a) identifying a respective risk zone of each page;

(b) selecting at least one unwritten page for writing new data; and

(c) for each said unwritten page whose risk zone includes at least one written page, copying each said written page to a log.

2. The method of claim 1, further comprising the step of:

(d) writing said new data to said at least one unwritten page.

3. The method of claim 2, wherein, if said new data span more than one page, said writing is effected substantially simultaneously.

4. The method of claim 2, wherein said copying and said writing are effected substantially simultaneously.

5. The method of claim 2, further comprising the steps of:

(e) checking whether data stored in at least one written page are corrupt; and

(f) if said data are corrupt, replacing said data with corresponding data from said log.

6. The method of claim 5, wherein said checking is effected using an error detection code.

7. The method of claim 5, wherein said checking and said replacing are effected when a system that includes the memory is powered up.

8. The method of claim 2, wherein said new data that are written to an unwritten page are written to said unwritten page only after every written page of said risk zone of said unwritten page have been copied to said log, the method further comprising the steps of:

for each written page that is copied to said log;

(e) setting a corresponding flag; and

(f) after said new data, that are to be written to said at least one unwritten page whose risk zone includes said each written page, have been written to every said at least one unwritten page whose risk zone includes said each written page;

clearing said corresponding flag.

9. The method of claim 8, further comprising the step of:

(g) for each said flag that is set;

replacing data stored in said written page that corresponds to said each flag with corresponding data from said log.

10. The method of claim 9, wherein said replacing is effected when a system that includes the memory is powered up.

11. The method of claim 2, wherein, if said new data span more than one page, said selected unwritten pages are written sequentially.

12. The method of claim 2, wherein, if said new data span more than one page, said selected unwritten pages are written in a random order.

13. The method of claim 2, wherein said copying and said writing are effected using different respective writing modes.

14. The method of claim 13, wherein said writing mode of said copying writes fewer bits to a cell of the memory than said writing mode of said writing.

15. The method of claim 1, wherein all said risk zones include an equal number of pages.

16. The method of claim 15, wherein each said risk zone includes one page.

17. The method of claim 1, wherein at least two said risk zones include different numbers of pages.

18. A data storage system, comprising:

(a) a data storage medium including a plurality of pages;

(b) a log; and

(c) a controller for writing new data to said plurality of pages by steps including;

(i) identifying a respective risk zone of each page of said plurality of pages;

(ii) selecting at least one unwritten page of said plurality of pages for writing said new data; and

(iii) for each said unwritten page whose risk zone includes at least one written page of said plurality of pages, copying each said written page to said log.

19. The data storage system of claim 18, wherein said data storage medium is non-volatile.

20. The data storage system of claim 19, wherein said data storage medium is a flash memory.

21. The data storage system of claim 20, wherein said flash memory includes a plurality of multi-level cells.

22. The data storage system of claim 20, wherein said flash memory includes a plurality of blocks, such that each block of said plurality of blocks includes a respective subplurality of said plurality of pages, and wherein said controller writes said new data to said pages of each said block only sequentially.

23. The data storage system of claim 20, wherein said flash memory includes a plurality of blocks, such that each block of said plurality of blocks includes a respective subplurality of said plurality of pages, and wherein said controller writes said new data to said pages of each said block in a random order.

24. The data storage system of claim 18, wherein said log is part of said data storage medium.

25. The data storage system of claim 18, wherein said controller writes said new data to said plurality of pages by steps further including:

(iv) writing said new data to said at least one unwritten page of said plurality of pages.

26. The data storage system of claim 25, wherein said copying to said log and said writing to said at least one unwritten page are effected using different respective writing modes.

27. The data storage system of claim 26, wherein said writing mode of said copying to said log writes fewer bits to a cell of said data storage medium than said writing mode of said writing to said at least one unwritten page.

28. A computer-readable storage medium having computer-readable code embedded in the computer-readable storage medium, the computer readable code for writing new data to at least one of a plurality of pages of a data storage medium, the computer-readable code comprising:

(a) program code for identifying a respective risk zone of each page;

(b) program code for selecting at least one unwritten page for writing new data; and

(c) program code for, for each said unwritten page whose risk zone includes at least one written page, copying each said written page to a log.