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Frequently-redundant array of independent disks

Patent 5720025 Issued on February 17, 1998. Estimated Expiration Date: Icon_subject January 18, 2016. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.

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Inventors

Application

No. 588140 filed on 01/18/1996

US Classes:

714/6Redundant stored data accessed (e.g., duplicated data, error correction coded data, or other parity-type data)

Examiners

Primary: Beausoliel, Robert W. Jr.
Assistant: Baderman, Scott

International Class

G06F 011/14

Abstract

There is provided a method and apparatus for effectuating data updates on a fault-tolerant storage device having a plurality of disk-drive units forming a disk array, with parity-block updates temporarily suspended to provide increased performance. Parity-block updates are typically deferred until the array is idle. Thus, data is written onto the array with no parity error correction information being present for a short amount of time. Data updates are effectuated by identifying the blocks in the array where data is to be written. New data is then written directly to the identified blocks without reading the old data present therein. A "needs parity rebuild bit" (NPRB) is written to non-volatile memory, identifying the stripes not having parity information on the array. The number of NPRBs present is monitored to allow continuous calculation of a mean-time-to-data-loss (MTTDL). If the MTTDL is acceptable, parity updates are deferred until the array is idle. To that end, the I/O patterns to and from the array are monitored to determine idleness. If the I/O patterns indicate that the disk array is idle, new data is read and parity information is generated which is then written to the array.

Other References

  • Gibson et al., "Failure Correction Techniques for Large Disk Arrays", 1989, pp. 123-132, Association for Computing Machinery
  • Cormen et al., "Integrating Theory and Practice in Parallel File Systems," Proceedings of the DAGS '93 Symposium, Jun. 21-23, 1993, pp. 64-74
  • Stodosky et al. "Parity Logging: Overcoming the Small Write Problem in Redundant Disk Arrays," Proceedings 20th International Symposium on Computer Architecture, May 16-19, 1993, pp. 64-75
  • Menon et al., "Methods for Improved Update Performance of Disk Arrays," IBM report RJ 6928 (66034), Jul. 13, 198
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