Browse Prior Art Database

Individual Surface Banding in Direct Access Storage Devices

IP.com Disclosure Number: IPCOM000113064D
Original Publication Date: 1994-Jul-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Cunningham, EA: AUTHOR

Abstract

A method is disclosed to obtain higher capacity and reliability on multi-headed Direct Access Storage Devices (DASD) using individual banding on each surface instead of the standard fixed banding.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Individual Surface Banding in Direct Access Storage Devices

      A method is disclosed to obtain higher capacity and reliability
on multi-headed Direct Access Storage Devices (DASD) using individual
banding on each surface instead of the standard fixed banding.

      The standard method of a DASD design that includes frequency
banding is to find the appropriate set of frequency and radial switch
points that will produce about the same error rate at the inner
tracks of each band.  For constant capacity on each DASD and for
simplicity, all units built have the same sets of frequencies and
switch point radii.  The differing capabilities of the head/disk
combinations cause the error rates on different surfaces to vary by
multiple orders of magnitude.  The error rate of the worst head/disk
combination then typically dominates the soft and hard error rates of
whole DASD.  The highest rate must therefore be limited to meet the
required error rate specifications.

      The larger the number of heads in the DASD, the higher the
probability of having one or more heads exceed the set limit.  Thus
DASD with many heads must be designed with a lower average error rate
to reduce the fallout due to high error rate components.

      However, if several higher frequency bands and one or a few
lower frequency bands are allowed, in addition to the normal bands,
then each head/disk combination can be separately optimized.  The few
high error rate head/disk combinations can use bands with somewhat
lower frequency and hence lower linear density, that is more
consistent with their capability and will then have the error rate of
that...