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Optimization of Storage Capacity on Storage Devices Supporting Variable Length Records with Fixed Block Length Medium Constraints

IP.com Disclosure Number: IPCOM000104128D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 4 page(s) / 186K

Publishing Venue

IBM

Related People

Mosser, HV: AUTHOR [+2]

Abstract

The recording format of certain storage devices and mediums requires a constraint that the recorded information have a fixed length block or a block which is some integral multiple of a fixed length. When the information block to be recorded does not exactly fit in the length required by the recording constraint, the device must somehow package the information block within the recorded block such that the recording constraint is met.

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This is the abbreviated version, containing approximately 31% of the total text.

Optimization of Storage Capacity on Storage Devices Supporting Variable Length Records with Fixed Block Length Medium Constraints

      The recording format of certain storage devices and mediums
requires a constraint that the recorded information have a fixed
length block or a block which is some integral multiple of a fixed
length.  When the information block to be recorded does not exactly
fit in the length required by the recording constraint, the device
must somehow package the information block within the recorded block
such that the recording constraint is met.

      A method utilized by some devices is to pad the information
block with recording patterns until the recording constraint is met.
The padded information, however, does not contain any information
which is usable by the user of the storage device and as such wastes
a certain amount of the effective storage capacity of the medium.

      In cases where the fixed block length (or integral multiple of
a fixed length) is large compared to the equivalent of about 64 bytes
of recorded information, an alternate solution to to this problem is
described which allows the recording constraint to be met and does
not significantly impact the capacity of the recording medium.

      This article describes a method to support variable length
information blocks on a recording medium which requires fixed length
recording in a manner which does not waste the storage capacity of
the device.  The technique was initially developed for use with a
tape device, but the concept is applicable to any device which has a
fixed length recording constraint.  Certain recording techniques may
require that the length of an information block to be recorded on the
medium meet certain length constraints.  In order to meet these
constraints, an information block which does not meet these
constraints must be processed in a way that the information block
which is recorded does in fact meet the constraint.  To examine
various techniques to address the problem, assume a device which
requires that any record information block be exactly 8K bytes long.

      Padding is a technique which causes additional null data to be
stored at the end of an information block in order to make the length
of the information block match the constraint.  Using a padding
technique to meet the recording constraint, recording of, for
example, a 1K block with padding would require the utilization of 8K
worth of storage capacity of the recording medium.  Records larger
than 8K might be processed by splitting the information block into
parts which are 8K or smaller in size and storing them in multiple
storage regions.  Recording of, for example, a 9K block would require
16K worth of storage capacity of the recording medium, using two
storage regions.

      Auto-blocking is a technique which packages multiple
information blocks into a single physical block for recording on the
medium.  With auto-blocking, e...