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Two Means of Improving Access to the Data in a Library Subsystem

IP.com Disclosure Number: IPCOM000120229D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 78K

Publishing Venue

IBM

Related People

Greenberg, D: AUTHOR [+2]

Abstract

This article offers two means of improving the accessibility to the data in a library subsystem. In such a library subsystem, data is organized by cartridges stored in distinct sets of boxes or modules. Each of these modules has one or two robotic cartridge pickers. These are used to load cartridges into internal drives and then to unload and return the cartridges to their storage slots. The cartridges themselves may contain optical, magnetic, or any other recording medium.

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This is the abbreviated version, containing approximately 52% of the total text.

Two Means of Improving Access to the Data in a Library Subsystem

      This article offers two means of improving the
accessibility to the data in a library subsystem.  In such a library
subsystem, data is organized by cartridges stored in distinct sets of
boxes or modules.  Each of these modules has one or two robotic
cartridge pickers.  These are used to load cartridges into internal
drives and then to unload and return the cartridges to their storage
slots.  The cartridges themselves may contain optical, magnetic, or
any other recording medium.

      Usage patterns indicate that the workload is not uniformly
distributed across the cartridges.  Usage is affected by a strong
time dependency, namely that the freshest data is the most frequently
retrieved.  This time dependency skews the workload so that up to 80%
of the workload can be handled by 20% of the cartridges in a module.

      This article addresses library subsystems which do not have
robotic pass-through of the physical cartridge between modules.  We
advocate the use of a dual copy of the most frequently used (MFU)
cartridges as a means of improving the accessibility to these
cartridges.  In a given subsystem, the dual copies would be dispersed
via softcopy to the other modules.  A dual copy of a MFU cartridge
would then offer a second path to the data when the primary copy was
denied access in a heavily utilized or saturated library module.

      To determine the MFU set, do the following.  First, track the
number of inquiries to each cartridge in each optical library module
over a time period, such as a week. Select the top N% of the
cartridges which received inquiries in that period.  These cartridges
would be deemed the MFU cartridges.  The value of N could be adjusted
by the system programmers between a...