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Managing data storage devices connected to a digital computer

  • US 4,638,424 A
  • Filed: 01/12/1984
  • Issued: 01/20/1987
  • Est. Priority Date: 01/12/1984
  • Status: Expired due to Term
First Claim
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1. In the machine-implemented method of operating a data-storage hierarchy having a plurality of primary and secondary data-storage volumes, each of said volumes being addressable and having a given plurality of addressable data-storage areas for respectively storing a predetermined amount of data, each of said primary volumes having relatively rapid-access characteristics for data stored therein while each of said secondary volumes having relatively slow access characteristics for data stored therein, means coupled to said volume for transferring data therebetween;

  • including the steps of;

    transferring data from a first one of said secondary volumes to a first one of said primary volumes for constituting a recall of data stored in said first one secondary volume;

    transferring data from a second one of said primary volumes to a second one of said secondary volumes for constituting a migration of data stored in said second one primary volume;

    initiating a one of a said migrations of data and a one of said recalls of data, respectively, as a migration step and as a recall step;

    upon initiating each said migration step, first determining the accessibility of said second one of said secondary volumes which is to receive and store data to be migrated, upon determining said second one of said secondary volumes is accessible, performing said migration step;

    upon determining that said second one of said secondary volumes is not accessible, assigning a third one of said secondary volumes to receive and store said data to be migrated and then performing said migration step to said third one of said secondary volumes;

    upon initiating a said recell step, first determining the accessibility of said first one of said secondary volumes, if said first one of said secondary volumes is accessible, then performing said recall step, otherwise setting a flag bit indicating that the initiated recall is being delayed;

    during said migration step, repeatedly sensing said flag bit for determining if a recall is being delayed;

    when said flag bit is reset, continuing said migration step, otherwise when the flag bit is set, determining if said second one of said secondary volumes is to be said first one of said secondary volumes;

    if not, continuing the migration step, otherwise selecting a fourth one of said secondary volumes to receive a remaining portion of the data to be migrated and continuing said migration step with said fourth one of said secondary volumes for receiving and storing said remaining portion; and

    then performing said recall step with said second one of said secondary volumes.

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