Browse Prior Art Database

Automatic Cartridge Facility Usage in a 3495 Library

IP.com Disclosure Number: IPCOM000118144D
Original Publication Date: 1996-Oct-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 106K

Publishing Venue

IBM

Related People

Peake, JW: AUTHOR

Abstract

Disclosed is a method for balancing the use of the Automatic Cartridge Facility on the IBM* 3590 tape device between caching scratch cartridges and the most recently used cartridges in an automated library.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Automatic Cartridge Facility Usage in a 3495 Library

      Disclosed is a method for balancing the use of the Automatic
Cartridge Facility on the IBM* 3590 tape device between caching
scratch cartridges and the most recently used cartridges in an
automated library.

      The method utilizes the random access capabilities of the
automatic cartridge of the IBM 3590 facility to balance the following
operational needs:
  o  Maintain enough scratch volumes in the automatic cartridge
      facility of a tape device to almost always be able to
      satisfy a scratch mount request without having to wait to
      move a cartridge from rack storage as workload and
      scratch/specific mount request ratios change.
  o  Keep as many of the most active volumes in the automatic
      cartridge facility as possible to enable fast reload when
      requested.

      The method to provide the balancing is to break up the 10
physical positions in the automatic cartridge facility on each drive
into two groups, those allocated to scratch volumes (N) and those
allocated to the most recently accessed group (M).  M always is equal
to 10 - N.  N will vary as the workload and the ratio of scratch to
specific mounts changes over a period of time.  The algorithm to
deteremine N is as follows:
  1.  Start with a base value of N for a drive.  A base value of
       2 is a good place to start.  The goal is to keep N scratch
       cartridges available in the automatic cartridge facility.
  2.  Whenever a scratch mount request is received for the drive,
       the library manager that controls the IBM 3495 Tape Library
       Dataserver instructs the drive to load one of the available
       scratch cartridges from the automatic cartridge facility
       and schedules a new scratch cartridge to be moved from the
       storage racks to the drive.  When a scratch mount can be
       satisfied by the automatic cartridge facility, it is called
       a scratch hit.  If scratch hits occur for two subsequent
       scratch mounts in a row for a drive, the value of N is
       decremented by 1 until it reaches the base value (2 in
       this example).
  3.  If no scratch cartridges are available in the automatic
       cartridge facility, a scratch miss has occurred and the
       robotics must be used to satisfy the scratch mount.
  4.  When a scratch miss occurs for two subsequent scratch
       mounts in a row for a drive, the value of N is incremented
       by 1.  Since N has been incremented, the library manager
       schedules an additional cartridge to be brought over to
       the drives automatic cartridge facility.
  5.  By keeping trac...