System and method for reducing data loss in disk arrays by establishing data redundancy on demand

• US 20050091452A1
• Filed: 10/28/2003
• Published: 04/28/2005
• Est. Priority Date: 10/28/2003
• Status: Abandoned Application

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Hsu, Windsor W., Young, Honest C., Chen, Ying
• Application Number:
  US10/695,475
• Publication Number:
  US 20050091452A1
• Time in Patent Office: Days
• US Class Current: 711/114
• CPC Class Codes: G06F 11/1076 Parity data used in redundant arrays of independent storages, e.g. in RAID systems
• CPC Class Codes: G06F 2211/1054 Parity-fast hardware, i.e. dedicated fast hardware for RAID systems with parity

Abstract

Disclosed is a system and method for reducing data loss in a disk array comprising computing redundant data of the user data in the disk array, periodically storing the computed redundant data into data blocks located on at least one disk; monitoring the disks for a number of concurrent actual and predicted disk failures to occur; determining which portions of the redundant data have been altered since an immediate previous time the redundant data was stored; re-computing altered portions of the redundant data and updating the corresponding data blocks when said number of concurrent disk failures occur and less than a fraction of the redundant data has been altered, reconstructing data stored on a failed disk onto at least one replacement disk; and marking the recomputed redundant data in a directory, wherein the disk array comprises one of the standard RAID arrays.

Claims

1. A method for reliably storing data on disks, said method comprising:

writing a data block to be stored in a disk array;

combining an address of said data block to a set of retrievable addresses;

periodically computing a function of said data stored in said disk array;

storing the computed function on at least one spare disk;

on a disk failure in said disk array, updating the computed function using said set of retrievable addresses to recompute only altered portions of said function; and

deleting said set of retrievable addresses.

2. The method of claim 1, wherein said disk failure includes disk failures that are predicted to occur.

3. The method of claim 1, wherein said function comprises a mathematical function.

4. The method of claim 1, wherein said function comprises an error correcting code.

5. The method of claim 1, wherein said address of said data block comprises an address of a corresponding portion of the computed function and said set of retrievable addresses comprises a set of addresses that describe portions of the computed function requiring updating.

6. The method of claim 1, wherein said disk array comprises at least one a RAID array.

7. The method of claim 1, further comprising reconstructing data stored on a failed disk onto at least one replacement disk.

8. The method of claim 1, wherein said steps of updating and deleting are skipped if said set of retrievable addresses exceeds a fraction of said data stored in said disk array.

9. The method of claim 1, wherein altered portions of said computed function are updated whenever a load on said disk array is below a threshold value.

10. The method of claim 1, wherein altered portions of said computed function that are less likely to be altered again are preferentially updated.

11. A method of reducing data loss in a disk array, said method comprising:

periodically storing redundant data into data blocks located on a spare disk;

monitoring said disks in said disk array for disk failures to occur;

determining which of said data blocks contain redundant data that has been altered since an immediate previous time said redundant data was stored;

recomputing altered portions of said redundant data; and

storing the recomputed altered portions in said data blocks.

12. The method of claim 11, wherein said disk failures include disk failures that are predicted to occur.

13. The method of claim 11, further comprising updating said data blocks with altered redundant data when said disk failures have occurred.

14. The method of claim 11, wherein said disk array comprises at least one a RAID array.

15. The method of claim 11, further comprising reconstructing data stored on a failed disk onto at least one replacement disk.

16. The method of claim 13, wherein said step of updating said data blocks comprising altered redundant data is skipped if a number of said data blocks exceeds a fraction of said data stored in said disk array.

17. The method of claim 12, wherein said data blocks containing altered redundant data are updated whenever the load on the disk array is below a threshold value.

18. The method of claim 17, wherein the data blocks containing altered redundant data that is less likely to be altered again are preferentially updated.

19. A system for reducing data loss in a disk array comprising:

a storage unit operable for periodically storing redundant data into data blocks located on a spare disk;

a monitor operable for monitoring the disks in the array for disk failures to occur;

a directory operable for determining which of said data blocks contain redundant data that has been altered since an immediate previous time said redundant data was stored; and

a computer operable for updating only portions of said redundant data that has been altered.

20. The system of claim 19, wherein said disk failures monitored include disk failures that are predicted to occur.

21. The system of claim 19, further comprising a controller operable for updating said redundant data when said disk failures have occurred.

22. The system of claim 19, further comprising at least one replacement disk operable for storing reconstructed data previously stored on a failed disk.

23. The system of claim 19, wherein said directory is operable for marking the recomputed redundant data in said directory.

24. The system of claim 19, wherein said disk array comprises at least one a RAID array.

25. The system of claim 19, further comprising a controller operable for updating said redundant data whenever a load on said disk array is below a threshold value.

26. The system of claim 25, wherein said controller preferentially updates redundant data that is less likely to be altered again.

27. A system of reducing data loss in a disk array comprising:

means for periodically storing redundant data into data blocks located on a spare disk;

means for monitoring said disk for disk failures to occur;

means for determining which of said data blocks contain redundant data that has been altered since an immediate previous time said redundant data was stored;

means for recomputing altered portions of said redundant data in said data blocks; and

means for storing the recomputed altered portions in said data blocks.