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Adaptive Override of Middle of Tape Rewind for Libraries with Two-Reel Cassettes

IP.com Disclosure Number: IPCOM000115715D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Winarski, DJ: AUTHOR

Abstract

In an automated library of two-reel cassettes, it is advantageous to have the load point of the tape be the Middle of Tape (MOT). However, it is not always advantageous to rewind the tape to MOT before unloading each cassette from its respective drive.

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

Adaptive Override of Middle of Tape Rewind for Libraries with Two-Reel
Cassettes

      In an automated library of two-reel cassettes, it is
advantageous to have the load point of the tape be the Middle of Tape
(MOT).  However, it is not always advantageous to rewind the tape to
MOT before unloading each cassette from its respective drive.

      If MOT is the load point of a two-reel cassette, then the first
random seek will be one quarter of the length of the tape, a distance
which is half way to either end of the tape.  If either end of the
tape had been used as the load point, the first random seek would be
one half of the length of the tape.  This means that less time will
be spent doing the initial seek if the load point is at MOT, a fact
which makes it highly advantageous to use MOT as the load point for a
two-reel cassette.

      If it is required to rewind or preposition the tape to MOT
before unloading the two-reel cassette from its drive, this could
cause a delay in the servicing of the next mount request when the
library is drive-bound.  When a new mount request is pending, this
article improves the performance of a drive-bound library by
deferring the rewind to MOT for a cleanup cycle to be undertaken
during lull periods in library activity.

      When a library is drive-bound, a queue of mount requests will
form.  When such a mount queue exists, it is proposed that the rewind
to MOT on a mounted cassette be deferred in favor of speeding up the
mounting of the next cassette.  Any cassettes so demounted before
being rewound to MOT can be tagged by the control unit or host for
later remount and rewinding to MOT when the library workload has
returned to a lower level.

      This delaying of rewind to MOT is unique to tape libraries with
two-reel cassettes.  Optical disks must be spun down prior to
dismount...