Method and system for facilitating fast wake-up of a flash memory system

• US 20060253645A1
• Filed: 05/08/2006
• Published: 11/09/2006
• Est. Priority Date: 05/09/2005
• Status: Active Grant

• Current Assignee: SanDisk IL Ltd. (Western Digital Corporation)
• Original Assignee: M-Systems Flash Disk Pioneers Ltd. (Western Digital Corporation)
• Inventors: Lasser, Menahem
• Granted Patent: US 8,244,958 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory

Abstract

Methods, systems and computer-readable code for maintaining flash data structures in accordance with events of a flash memory system are disclosed. Both an events log as well as at least one flash management table are maintained in flash memory. For at least one point in time, a most recently stored flash memory table is indicative of an earlier state of the flash memory system, while at least one event that is more recent than the earlier state is stored in the events log. During power-up, the flash management table is retrieved from flash memory. If the most recent event of the flash memory table is earlier than the most recent event of the events log, events are retrieved from the events log in order to update the flash memory table. Optionally, the updated flash memory table is saved to flash memory.

Claims

1. ) A method of maintaining flash data structures in accordance with events of a flash memory system, the method comprising

a) maintaining in flash memory at least one flash management table whose contents are indicative of a state of the flash memory system;

b) maintaining in said flash memory an events log, wherein, for at least one point in time,

i) a most recently stored said at least one flash management table is indicative of an earlier state of the flash memory system; and

ii) at least one event more recent than said earlier state is stored in said events log.

2. ) The method of claim 1 wherein for said at least one point in time a most recent event is stored in said events log.

3. ) The method of claim 1 wherein for said at least one point in time a current state of the flash memory system is reflected by contents of said stored events log and said stored at least one flash management table.

4. ) The method of claim 2 further comprising

c) generating from said at least one table indicative of said earlier state and from said events log at least one table indicative of a more current state of the flash memory system.

5. ) The method of claim 4 wherein said more current state is a most current state of the flash memory system at a time of said generating.

6. ) The method of claim 4 wherein said generating is effected when waking up.

7. ) The method of claim 1 wherein said maintaining of said at least one management table includes, at another point in time distinct from said at least one point in time, synchronizing said at least one flash management table to a latest recorded event of said events log.

8. ) The method of claim 1 wherein said maintaining of said at least one flash management table in said flash memory includes periodically synchronizing in said flash memory said at least one flash management table to a current state.

9. ) The method of claim 1 wherein said maintaining of said at least one flash management table in said flash memory includes, for every Nth change of state of the flash memory system, synchronizing in said flash memory said at least one flash management table to a current state, wherein N>

=2.

10. ) The method of claim 1 wherein said maintaining of said at least one flash management table in said flash memory includes:

i) upon occurrence of a change of state of a first pre-determined type, synchronizing in said flash memory said at least one flash management table to a current state; and

ii) upon occurrence of a change of state of a second pre-determined type, not synchronizing in said flash memory said at least one flash management table to said current state.

11. ) The method of claim 1 wherein a frequency for which said at least one flash management table is updated in said flash memory is determined in accordance with an availability of resources of the flash memory system.

12. ) The method of claim 1 wherein said at least one flash management table includes a translation table which maps virtual block numbers into physical block numbers.

13. ) The method of claim 1 wherein said at least one flash management table includes a free blocks table.

14. ) The method of claim 1 wherein said maintaining includes maintaining a plurality of said flash management tables in said flash memory.

15. ) The method of claim 1 wherein said maintaining in said flash memory of an events log includes writing data to said flash memory using a faster writing mode of said flash memory.

16. ) The method of claim 1 wherein said flash memory provides both MLC and SLC modes, and said maintaining in said flash memory of an events log is carried out using said SLC mode.

17. ) The method of claim 1 wherein said maintaining of said log is carried out as part of caching operations of the flash memory system.

18. ) A method of waking up in a flash memory system, the method comprising:

I) When waking up,

a) reading from flash memory at least one flash management table describing a state of the flash memory system;

b) reading from said flash memory an events log containing records of pre-stored events of the flash memory system;

c) for at least one event stored in said events log, updating said at least one flash management table in accordance with changes effected by said at least one event.

19. ) The method of claim 18 wherein said updating is repeated until said at least one flash management table is updated in accordance with a most recent event of said events log.

20. ) The method of claim 18 wherein said at least one flash management table includes a translation table which maps virtual block numbers into physical block numbers.

21. ) The method of claim 18 wherein said at least one flash management table includes a free blocks table.

22. ) The method of claim 18 wherein a plurality of said flash management tables are read from said flash memory and updated.

23. ) A flash memory system comprising:

a) a flash memory for storing data; and

b) flash management software for maintaining data structures used for accessing said flash memory,

wherein said flash management software is operative to;

i) maintain in said flash memory at least one flash management table whose contents are indicative of a state of the flash memory system; and

b) maintain in said flash memory an events log, such that, for at least one point in time,

I) a most recently stored said at least one flash management table is indicative of an earlier state of the flash memory system; and

II) at least one event more recent than said earlier state is stored in said events log.

24. ) A flash memory system comprising:

a) a flash memory for storing data; and

b) flash management software for maintaining at least one data structure used for accessing said flash memory,

wherein, when waking up, said flash management software is operative to;

i) read from flash memory at least one flash management table describing a state of the flash memory system;

ii) read from said flash memory an events log containing records of pre-stored events of the flash memory system;

iii) for at least one event stored in said events log, update said at least one flash management table in accordance with changes effected by said at least one event.

25. ) A computer readable storage medium having computer readable code embodied in said computer readable storage medium, said computer readable code comprising instructions for maintaining flash data structures in accordance with events of a flash memory system, wherein said instructions comprise instructions to:

a) maintain in flash memory at least one flash management table whose contents are indicative of a state of the flash memory system;

b) maintain in said flash memory an events log, wherein, for at least one point in time,

i) a most recently stored said at least one flash management table is indicative of an earlier state of the flash memory system; and

ii) at least one event more recent than said earlier state is stored in said events log.

26. ) A computer readable storage medium having computer readable code embodied in said computer readable storage medium, said computer readable code comprising instructions for maintaining flash data structures in accordance with events of a flash memory system, wherein said instructions comprise instructions to:

I) When waking up,

a) read from flash memory at least one flash management table describing a state of the flash memory system;

b) read from said flash memory an events log containing records of pre-stored events of the flash memory system;

c) for at least one event stored in said events log, update said at least one flash management table in accordance with changes effected by said at least one event.

27. ) A method of maintaining flash data structures in accordance with events of a flash memory system, the method comprising:

a) maintaining in flash memory at least one flash management table whose contents are indicative of a state of the flash memory system;

b) maintaining in said flash memory an events log; and

c) concurrent with said maintaining of said at least one flash management table, maintaining in said flash memory data uniquely identifying a specific event of said events log, wherein said specific event is a most recent event corresponding to said contents of said at least one table.