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Method and means for distributed sparing in DASD arrays

  • US 5,258,984 A
  • Filed: 06/13/1991
  • Issued: 11/02/1993
  • Est. Priority Date: 06/13/1991
  • Status: Expired due to Term
First Claim
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1. In a storage subsystem having a plurality of DASDs, a method for rebuilding portions of parity groups resident on a failed one of said DASDs, each parity group including N data, P parity, and S spare blocks, each DASD storing K blocks, comprising the steps of:

  • (a) configuring an array of N+P+S DASDs;

    (b) distributing K parity groups in synchronous array addresses across subsets of N+P DASDs of the array such that no two blocks from the same parity group reside on the same DASD, each DASD storing data or parity blocks from (K-K*S/N+P+S)) parity groups, and distributing K*S blocks as spare storage across the array such that each DASD includes K*S/(N+P+S) spare blocks thereon; and

    (c) in the event of a single DASD failure, for each of the K-K*S/(N+P+S) parity groups on the failed DASD, logically combining N+P+S-2 blocks belonging to the group from N+P+S-2 other DASDs into a single block, and, writing said single block into a counterpart one of the remaining K*S*(N+P+S-1)/(N+P+S) spare blocks such that no two blocks of the same parity group are distributed on the same DASD.

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