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Method and means for encoding and rebuilding the data contents of up to two unavailable DASDS in a DASD array using simple non-recursive diagonal and row parity

  • US 5,579,475 A
  • Filed: 08/24/1995
  • Issued: 11/26/1996
  • Est. Priority Date: 02/11/1991
  • Status: Expired due to Fees
First Claim
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1. A method for encoding and rebuilding of any data contents of up to two unavailable direct access storage devices (DASD'"'"'s) from an array of M failure independent DASDs and a plurality of DASDs operative as spares to said array of M failure independent DASDs and where a two DASD equivalent of spare space is distributed over said M failure independent DASDs, M being a prime number, said data contents being expressed as an (M-1)*(M-2) data block array, the blocks in each row of the data array being stored in counterpart ones of the DASDS forming the array of M failure independent DASDs, comprising the steps of:

  • (a) generating an (M-1)*M data block array from the (M-1)*(M-2) data block array by calculating non-recursive simple parity values over diagonal and row traverses of the (M-1)*(M-2) data block array, said parity values being calculated in respective diagonal major and row major order and being defined over a counterpart diagonal or row of said data block array, a parity mode (odd or even) of data blocks along a reference diagonal operating as a mode for calculating a parity value for non-reference diagonals, the parity value for each row being calculated according to an even mode;

    (b) writing the blocks in each row of said (M-1)*M data array to counterpart ones of said M failure independent DASDs; and

    (c) responsive to the availability of up to two DASDs, rebuilding any portion of said data array from not less than (M-2) available DASDs and writing said rebuilt portion either to counterpart spare DASDs or to spare space available on no less than M-2 remaining DASDs.

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