Power failure detection and correction in a flash memory device

• US 7,340,647 B2
• Filed: 04/06/2006
• Issued: 03/04/2008
• Est. Priority Date: 02/27/2002
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Aasheim, Jered, Kalkman, John, Yang, Yongqi
• Primary Examiner(s): MCCARTHY, CHRISTOPHER S
• Application Number:
  US11/278,861
• Publication Number:
  US 20060168474A1
• Time in Patent Office: 698 Days
• Field of Search: 714/14, 714/24, 714/35, 711/103
• US Class Current: 714/24
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 11/1474 in transactions G06F16/20 takes precedence
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 16/10 File systems; File servers
• CPC Class Codes: G06F 2212/7201 Logical to physical mapping or translation of blocks or pages
• CPC Class Codes: G06F 2212/7207 management of metadata or control data
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/0643 Management of files
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99955 Archiving or backup

Abstract

A transactional file system developed to function with flash memory is described. The file system performs power-failure detection and ensures data integrity in the event of a power failure. In one described implementation, a power failure event can be detected by a file system, components of the file system, or individual modules in the form or computer-executable instructions and/or logic. Meta-information is stored at a location on a flash medium indicated by a write pointer if a computer device shuts-down according to a normal shutdown mode. During initialization of the computer, a check is performed whether the meta-information is present in the location on the flash medium indicated by the write pointer. If the meta-information is present, then a conclusion is made that the computer shutdown according to the normal shutdown mode.

Claims

1. In a computer having a flash medium, a method for ensuring data integrity in a flash medium, comprising:

organizing a flash memory medium as if memory locations of the flash memory form a continuous circle, wherein the lowest and highest memory locations are contiguous;

maintaining a write pointer to indicate a memory location that is free to receive new data, the write pointer configured to advance through the continuous circle of memory locations as data is written to the flash memory medium;

storing meta-information in each memory location indicated by the write pointer at completion of a write operation to the memory location indicated by the write pointer;

searching the memory location indicated by the write pointer when the file system is initialized to ascertain whether the meta-information exists in the memory location;

concluding that a power-failure event occurred, if the meta-information is not found in the memory location; and

marking the memory location indicated by the write pointer dirty if a power-failure event is concluded.

2. The method as recited in claim 1, wherein the meta-information is a bit in the memory location that is marked active at completion of the write operation.

3. The method as recited in claim 1, wherein the write pointer is a component of a file system.

4. The method as recited in claim 1, wherein the memory locations are physical sector addresses.

5. The method as recited in claim 1, further comprising advancing the write pointer at least one memory location at a time at completion of a write operation.

6. The method as recited in claim 5, wherein advancing comprises advancing the write pointer from a lowest memory location to a highest memory location and repeating from the lowest memory location once the highest memory location is reached.

7. The method as recited in claim 5, wherein advancing comprises advancing the write pointer from a highest memory location to a lowest memory location and repeating from the highest memory location once the lowest memory location is reached.

8. The method as recited in claim 1, further comprising providing a next memory location address to store data, upon receiving a write request.

9. A file system, comprising:

sector management means for organizing a flash memory medium as if memory locations of the flash memory form a continuous circle, wherein the lowest and highest memory locations are contiguous;

the sector management means comprising write pointing means that indicate a memory location that is free to receive new data, the write pointing means configured to advance through the continuous circle a memory location at a time as data is written to the flash memory medium; and

power failure management means configured to store data valid information in each memory location indicated by the write pointing means at completion of writing data into each memory location, wherein the power failure management means is further configured to (i) search the memory location indicated by the write pointing means for the data valid information when the file system is initialized; and

(ii) mark the memory location dirty, if the data valid information is not found.

10. The file system as recited in claim 9, wherein the memory locations are physical sector addresses.

11. The file system as recited in claim 9, wherein the memory locations arc physical sector addresses and the write pointing means advances at least a physical sector address each time data is written on the flash memory medium.

12. The file system as recited in claim 9, wherein the sector management means contains at least one counter that is incremented to advance the write pointing means from the lowest memory location to the highest memory location and repeat counting once the highest memory location is reached.

13. The file system as recited in claim 9, wherein the sector management means contains at least one counter that is decremented to advance the write pointing means from the highest memory location to the lowest memory location and repeat decrementing once the lowest memory location is reached.

14. One or more computer-readable media comprising computer executable instructions that, when executed, direct a computer to:

maintain a write pointer to advance through a circular sequence of memory locations in the flash medium indicating a memory location that is available to receive data as the write pointer advances;

write data into the memory location indicated by the write pointer;

write metadata into the memory location indicated by the write pointer if the writing of data into the memory location is completed;

search the memory location indicated by the write pointer to determine whether the metadata exists in the memory location upon initializing the computer; and

mark the memory location indicated by the write pointer dirty, if the metadata does not exist in the memory location.

15. One or more computer-readable media as recited in claim 14, further comprising computer executable instructions that, when executed, direct the computer to conclude that a power-failure event occurred to the computer prior to completing the writing of data, if the metadata is not found by the search.

16. One or more computer-readable media as recited in claim 14, wherein the metadata is a bit in the memory location that is marked active each time writing of data into a memory location is completed and remains inactive each time the writing of data into a memory location is interrupted by a power-failure event.

17. One or more computer-readable media as recited in claim 14, wherein the memory locations are physical sector addresses.

18. One or more computer-readable media as recited in claim 14, wherein the metadata is a bit that remains inactive if the computer does not shutdown according to the normal shutdown mode.

19. One or more computer-readable media as recited in claim 14, wherein the metadata is a bit that is marked active each time the computer shuts-down according to the normal shutdown mode.

20. One or more computer-readable media as recited in claim 14, wherein the computer executable instructions are components of a file system.