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System for managing log structured array (LSA) of DASDS by managing segment space availability and reclaiming regions of segments using garbage collection procedure

  • US 5,551,003 A
  • Filed: 02/14/1994
  • Issued: 08/27/1996
  • Est. Priority Date: 12/11/1992
  • Status: Expired due to Fees
First Claim
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1. In a system having a segment-oriented and buffered log structured array (LSA) of DASDs, directory controlled means for establishing read and write access paths to logical tracks stored in said segments on said LSA as referenced by a source of external commands, cache means coupling the source and the LSA for separately read or write enqueuing the referenced logical tracks and for managing segment space availability by destaging tracks to the buffer of the LSA according to a usage discipline, and means for reclaiming regions of segments of the LSA by a garbage collection procedure, said reclaimed regions being available for recording segments formed from write modified logical tracks thereon, a method comprising the steps of:

  • (a) accumulating neighborhoods of tracks in the buffer in a destage path from the cache means and in a garbage collection path from the LSA, and performing read-activity-based sorting of the accumulated neighborhoods of tracks into corresponding segments formed from write modified read active logical tracks, write modified read inactive logical tracks, clean read active logical tracks, and clean inactive logical tracks;

    (b) writing segments from the buffer formed from write modified or clean read active tracks into an LSA DASD region of contiguous segments of read active tracks and writing segments from the buffer formed from write modified or clean read inactive tracks into an LSA DASD region of contiguous segments of read inactive tracks; and

    (c) ascertaining the number of free space segments in each region and garbage collecting segments having either free space, old write age, or read inactive tracks in the regions in the LSA where the detected number is less than a first threshold, continuing the collection until the number of collected segments exceeds a second threshold, and applying the collected segments to the garbage collection path.

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