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Array type disk system updating redundant data asynchronously with data access

  • US 5,761,402 A
  • Filed: 09/27/1994
  • Issued: 06/02/1998
  • Est. Priority Date: 03/08/1993
  • Status: Expired due to Term
First Claim
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1. An array type disk system, comprising:

  • a plurality of disk units, each of which includes a data area for storing data therein and a parity area for storing redundant data corresponding to the stored data therein, and which are arranged in the form of arrays and are operated in parallel;

    a disk control device which controls data accesses to respective disk units;

    a host computer system which commands the disk control device to access the respective disk units;

    update data generation means for generating update data by performing an exclusive OR operation between data before a write operation and data to be written when the data is to be first written into an address in a pertinent one of said disk units, and for generating new update data by performing an exclusive OR operation among the data before the write operation, the data to be written and the generated update data when the data is to be written into the address in the pertinent disk unit again, wherein the generation of update data utilizes a singular disk units;

    update data holding means for holding therein the update data generated by said update data generation means;

    log data generation means for generating a parity address as log data in association with the held update data, the parity address being that address of a particular one of said disk units at which redundant data for the data of the data address is stored;

    log data holding means, which includes a nonvolatile memory, for holding therein the log data generated by said log data generation means; and

    delayed parity generation means, operating asynchronously with the process of writing the data into said pertinent disk unit, for reading the redundant data associated with the update data out of the parity address of the particular disk unit in accordance with the parity address of the log data, for generating new redundant data on the basis of an exclusive OR operation performed on the redundant data read out of said particular disk unit in accordance with the parity address of the log data and the update data associated therewith from said update data holding means, and for writing the new redundant data into said particular disk unit in accordance with the parity address of the log data, wherein the generation of new redundant data utilizes a singular disk unit.

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