Browse Prior Art Database

Space Allocation on a Juke-Box Device

IP.com Disclosure Number: IPCOM000115766D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Barton, J: AUTHOR [+4]

Abstract

Disclosed is an optimal space allocation scheme for juke-box storage devices when logical volumes span physical platter boundaries and when there are a limited number of read/write heads.

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

Space Allocation on a Juke-Box Device

      Disclosed is an optimal space allocation scheme for juke-box
storage devices when logical volumes span physical platter boundaries
and when there are a limited number of read/write heads.

      A juke-box is a direct access storage device with a large
number of demountable platters partitioned into several logical
volumes, and a small number of read/write stations -- the mount
points.  A platter has to be mounted on a mount point before any I/O
can be performed to it.  If there are multiple platers per logical
volume, several mounts may be needed to read data from a logical
volume per I/O request.  In addition, if there is only one read/write
head per mount point, and the platter contains data on both surfaces,
the platter may also have to be flipped to read the opposite sides.

      These platter mount and flip operations constitute the I/O
overheads of a juke-box device.  These operations  typically take
several seconds to complete since they involve physical movements
like drive spin-down and spin-up, and fetching and returning of
platters.  To minimize the I/O overheads, any space allocation scheme
on a logical volume has to be sensitive to the physical platter
boundaries.  The scheme disclose here uses a cost function to prefer
allocations which assign space from fewer number of surfaces and from
fewer flip surfaces.

      Given a space allocation request, free space from a combination
of surfaces may be used to satisfy it.  Each su...