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Free Space Parameter for Magneto-optic Media

IP.com Disclosure Number: IPCOM000109406D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Dewey, DW: AUTHOR [+2]

Abstract

In file systems for standard Direct Access Storage Devices (DASDs) the "useability" of the free space can be measured by a defragmentation parameter. Specialized file systems for Magneto-Optic (MO) media, however, may have a second factor influencing the utility of the free space. This is the amount of the free space that is pre-erased.

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Free Space Parameter for Magneto-optic Media

       In file systems for standard Direct Access Storage
Devices (DASDs) the "useability" of the free space can be measured by
a defragmentation parameter.  Specialized file systems for
Magneto-Optic (MO) media, however, may have a second factor
influencing the utility of the free space.  This is the amount of the
free space that is pre-erased.

      Since allocations of new files from pre-erased space allows the
system to create files using a Write Verify (two-pass) operation
instead of an Erase Write Verify (three-pass) operation, it is
desirable to have as much of the free space pre-erased just as it is
desirable to have it in contiguous extents.

      We combine a measure of both these quantities into one
parameter.  The major advantage of this combination is that device
transparency is maintained by using only one parameter.  Existing
software and users already use a single parameter to initiate a
defrag utility.  By defining a parameter that combines a measure of
both fragmentation and the amount of erased space and creating a
defrag utility that erases the space as part of its operation,
storage management software does not need to treat the optic media
differently than DASD.  The resulting parameter may also be used by
intelligent library controllers for selecting volumes for background
defragging and erasing.

      The two measures are combined by first applying the standard
fragmentation parameter to optical media by treating sectors as
tracks.  The unerased space is th...