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Automated Cartridge Disposition Promotion (Unload-Least Recently Used to KEEP)

IP.com Disclosure Number: IPCOM000105649D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 4 page(s) / 98K

Publishing Venue

IBM

Related People

Power, RR: AUTHOR [+4]

Abstract

An automated media library uses one or more robotically controlled pickers to move data cartridges between storage slots and internal recording and/or playback devices. In libraries serviced by one single-gripper picker, preemptively Unloading the Least Recently Used (Unload_LRU) inactive volume can greatly speed the mounting of the next volume. However, time is wasted if that same preemptively demounted volume needs to be immediately remounted. The dilemma is when to KEEP inactive volumes mounted, to avoid thrashing, and when to make them eligible for preemptive unloading under Unload_LRU, to save time on the next mount request.

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Automated Cartridge Disposition Promotion (Unload-Least Recently Used to KEEP)

      An automated media library uses one or more robotically
controlled pickers to move data cartridges between storage slots and
internal recording and/or playback devices.  In libraries serviced by
one single-gripper picker, preemptively Unloading the Least Recently
Used (Unload_LRU) inactive volume can greatly speed the mounting of
the next volume.  However, time is wasted if that same preemptively
demounted volume needs to be immediately remounted.  The dilemma is
when to KEEP inactive volumes mounted, to avoid thrashing, and when
to make them eligible for preemptive unloading under Unload_LRU, to
save time on the next mount request.

      Included are three methods of assessing the proper volume
disposition, either KEEP or Unload_LRU.  In this article, volumes in
the library will have different dispositions and even the two volumes
which constitute the two sides of an optical disk cartridge could
have different dispositions.

      The preferred means of determining the proper disposition of
the individual optical volumes is by tracking the hit ratio of
individual volumes.  Volumes with a daily high hit ratio, say 4,
would earn the cartridge disposition of KEEP, as shown in Fig. 1.

      All other volumes would be deemed eligible for preemptive
unloading under Unload_LRU.  The hit ratio would be the ratio of the
number of accesses to that volume per unit time divided by the number
of mounts of that volume per that same time period.  Typically, one
day would be used as the sample time period, which would allow
reassessment of the individual volume dispositions frequently enough
for most customer needs.  The number of acceses and mounts per day
for each volume resident in the library box could be stored in the
control unit or host.  The time period for gathering statistics on
accesses and mounts could be menu selectable, as could the threshold
for the hit ratio.

      An alternative embodiment would involve the tracking of the
date of origination of the volume, i.e. when its first data was
stored on it.  This criteria would be more applicable to WORM optical
cartridges.  Young volumes should be given a disposition of KEEP, as
shown in Fig.  2.  This is because the resident data is invariably
st...