Browse Prior Art Database

Improved Disk Format for Parallel Head Disk Systems

IP.com Disclosure Number: IPCOM000115631D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 83K

Publishing Venue

IBM

Related People

Holleran, CR: AUTHOR [+2]

Abstract

Disclosed is a disk format that increases the efficiency of a parallel head disk drive design. The format eliminates the inherent inefficiency of parallel head designs through the use of a single ID FIELD to identify the data recorded on all tracks under a set of parallel heads.

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

Improved Disk Format for Parallel Head Disk Systems

      Disclosed is a disk format that increases the efficiency of a
parallel head disk drive design.  The format eliminates the inherent
inefficiency of parallel head designs through the use of a single ID
FIELD to identify the data recorded on all tracks under a set of
parallel heads.

      Traditionally, physical data elements stored on disk have at
least two unique fields.  An ID field contains the physical and
logical locator information to enable an orientation process to occur
after the movement of the disk arm.  Physical locator information in
the ID assures that the disk arm is over the right track.  Logical
locator information (usually a sequence number) assures that the disk
arm is over the right data element on the track.  A DATA field
associated with the ID field contains the user data.

      In addition to physical and logical locator information, the ID
field also is associated with servo information and so-called write
gap.  The servo information enables the disk electronics to locate
the ID in an otherwise random string of bits.  The write gap provides
time for the disk electronics to switch from reading to writing, if
necessary between the ID and DATA fields.  The overhead of an ID
field, for the purpose of this disclosure, includes the servo,
physical
locator and logical locator information as well as the write gap.

      When parallel heads are introduced to improve data transfer
times and/or availability  (RAID3), the typical solution entails
dividing up user data into n buffered chunks and reading them or
writing them in parallel.  ID fields and pad data which are
associated with each chunk are consistent such that each track has
the same number of fields and bytes--that is, each disk head
transfers the same number of information and control bytes.  In a
typical system with 128 bytes of ID field overhead and a user record
of 512 bytes, the efficiency with a single head is 512/(512+128)=
80%.  For a parallel head system with four heads, the efficiency is
(512/4)/((512/4)+128) = 50%.

      Alternatively,...