System and method for improving a data redundancy scheme in a solid state subsystem with additional metadata

• US 9,110,835 B1
• Filed: 03/17/2014
• Issued: 08/18/2015
• Est. Priority Date: 03/09/2011
• Status: Active Grant

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Call, Matthew, Morrison, John A., Phan, Lan D., Syu, Mei-Man L.
• Primary Examiner(s): KO, CHAE M
• Application Number:
  US14/216,919
• Time in Patent Office: 519 Days
• Field of Search: 714/6.11, 714/6.22, 714/6.24, 714/22
• US Class Current: 1/1
• CPC Class Codes: G06F 11/0727 in a storage system, e.g. in a DASD or network based storage system drivers for digital recording or reproducing units G06F3/06; circuits for error detection or correction within digital recording or reproducing units G11B20/18; for distributed storage of data in networks, e.g. transport arrangements for network file system [NFS], storage area networks [SAN] or network attached storage [NAS], H04L67/1097
• CPC Class Codes: G06F 11/0751 Error or fault detection not based on redundancy power supply failures G06F1/30; network fault management H04L41/06
• CPC Class Codes: G06F 11/108 Parity data distribution in semiconductor storages, e.g. in SSD
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: G06F 2211/104 Metadata, i.e. metadata associated with RAID systems with parity

Abstract

In one embodiment of the invention, a flash-based/solid-state storage system with an implemented data redundancy scheme such as RAID is configured to hold parity data in a volatile memory such as RAM and write such parity data to the non-volatile flash media when a full stripe of data has been written to the media. Other embodiments in certain situations force an early write of the parity for a partial stripe that has not been fully written to the non-volatile media. Those situations may include a data access error on data in a partial stripe and a detected power loss event with a partial stripe present. Embodiments are directed to writing additional data with the parity data for the partial stripe and then later using the additional data in data recovery. This approach allows the controller to easily detect the presence of a partial stripe and handle such a stripe accordingly.

Claims

1. A data storage system, comprising:

a non-volatile memory array configured to store a plurality of data stripes; and

a controller configured to;

in response to detecting a failure event, create a partial data stripe that comprises (1) metadata that specifies which of data elements of the partial data stripe are valid, (2) parity data, and (3) both valid and invalid data elements; and

use the metadata to determine which data elements of the partial data stripe are valid.

2. The data storage system of claim 1, wherein the controller is further configured to write the partial stripe to the non-volatile memory array.

3. The data storage system of claim 1, wherein the controller is further configured to:

recover at least one invalid data element using a valid data element and parity data; and

update the metadata to indicate that the at least one invalid data element has been recovered.

4. The data storage system of claim 3, wherein the controller is further configured to recover the at least one invalid data element using a plurality of valid data elements and parity data.

5. The data storage system of claim 3, wherein the controller is further configured to:

generate updated parity data based at least in part on the recovered data element; and

update the metadata to indicate that updated parity data has been generated.

6. The data storage system of claim 5, wherein the metadata comprises location information of data in the non-volatile memory array and the controller is configured to update the metadata to indicate that the parity data has been updated by indicating in the metadata location information of where the updated parity data is stored.

7. The data storage system of claim 1, wherein the metadata comprises a bit mask.

8. The data storage system of claim 1, wherein the failure event comprises at least one of a power failure event and a data access error from a data operation on the non-volatile memory array.

9. The data storage system of claim 8, wherein the controller is further configured to use the parity data and metadata to recover from the data access error.

10. The data storage system of claim 1, wherein the controller is further configured to use the metadata in a data relocation operation to determine which of the data elements in the partial data stripe are valid.

11. A method of recovering data stored in a data storage system, the method comprising:

in response to detecting a failure event, creating a partial data stripe that comprises (1) metadata that specifies which of data elements of the partial data stripe are valid, (2) parity data, and (3) both valid and invalid data elements;

writing the partial data stripe to a non-volatile memory array; and

using the metadata to determine which data elements of the partial data stripe are valid,

wherein the method is performed by a controller of the data storage system.

12. The method of claim 11, further comprising:

recovering at least one invalid data element using a valid data element and parity data; and

updating the metadata to indicate that the at least one invalid data element has been recovered.

13. The method of claim 12, wherein the metadata comprises location information of data in the non-volatile memory array and the method further comprises updating the metadata to indicate that the at least one invalid data element has been recovered by indicating in the metadata location information of where the recovered data element is stored.

14. The method of claim 12, wherein recovering the at least one invalid data element comprises using a plurality of valid data elements and parity data.

15. The method of claim 12, further comprising:

generating updated parity data based at least in part on the recovered data element; and

updating the metadata to indicate that updated parity data has been generated.

16. The method of claim 15, wherein the metadata comprises location information of data in the non-volatile memory array and the method further comprises updating the metadata to indicate that the parity data has been updated by indicating in the metadata location information of where the updated parity data is stored.

17. The method of claim 11, wherein the metadata comprises a bit mask.

18. The method of claim 11, wherein the failure event comprises at least one of a power failure event and a data access error from a data operation on the non-volatile memory array.

19. The method of claim 18, further comprising using the parity data and metadata to recover from the data access error.

20. The method of claim 11, further comprising using the metadata in a data relocation operation to determine which of the data elements in the partial data stripe are valid.