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Multiple Loading Zones Decrease Access Time in Tapes

IP.com Disclosure Number: IPCOM000110960D
Original Publication Date: 1994-Jan-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 95K

Publishing Venue

IBM

Related People

Prasad, MK: AUTHOR

Abstract

This article discloses a method for decreasing access time in tape subsystems which use cartridges (two spools in a package). Normally tapes have only one loading zone. The aim of this disclosure is to show that by having more than one loading zone, the average access time can be significantly reduced in multiple reads of the same tape. In addition, the total time that the tape stays in the drive is also reduced, thereby reducing the average service time in a tape library environment. Equivalently, for a given access or drive occupation time, the tape length can be increased or the tape velocity can be reduced, to give larger capacity.

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Multiple Loading Zones Decrease Access Time in Tapes

      This article discloses a method for decreasing access time in
tape subsystems which use cartridges (two spools in a package).
Normally tapes have only one loading zone.  The aim of this
disclosure is to show that by having more than one loading zone, the
average access time can be significantly reduced in multiple reads of
the same tape.  In addition, the total time that the tape stays in
the drive is also reduced, thereby reducing the average service time
in a tape library environment.  Equivalently, for a given access or
drive occupation time, the tape length can be increased or the tape
velocity can be reduced, to give larger capacity.

      Access time is critical in data storage applications where data
retrieval is not necessarily streamed.  In such cases, the time
required to position the head to read the data should be as small as
possible compared to the time required to read the data.  A typical
read operation consists of the following operations:

o   Movement of the head from its loading zone to the point where the
    data must be read.

o   Movement of the head to a loading zone.

      The loading zone is the area of the tape where the head should
be when the cartridge is loaded or unloaded.  It contains
initialization information such as servo and file statistics.  The
access and drive occupation time can be reduced by reducing the time
required for each of the actions listed above.  This article
discloses how this can be done by using more than one landing zone.

      Fig. 1 shows a stretched-out piece of tape of unit length with
L landing zones.  The tape length has been normalized to unity
without loss of generalization.  The relative motion of the tape is
modeled by keeping the tape stationary while the head moves.  The
relative head-tape velocity is v.  The access or drive occupation
time has two components:

o   Average time required to go from current to the desired position,
    denoted t seek.

o   Average time required to go from desired position to the nearing
    landing zone, denoted t sub load

      Because the head-tape...