Browse Prior Art Database

Transparently Present Multiple Physical Disk Media as Single Disk

IP.com Disclosure Number: IPCOM000114018D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 97K

Publishing Venue

IBM

Related People

Lybrand, DP: AUTHOR

Abstract

Described is a software implementation to provide transparently present multiple physical disks to a personal computer system as if they were a single disk. The implementation is designed to eliminate hardware limitations that prevent access to physical disk storage media as a result of size limitations.

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

Transparently Present Multiple Physical Disk Media as Single Disk

      Described is a software implementation to provide transparently
present multiple physical disks to a personal computer system as if
they were a single disk.  The implementation is designed to eliminate
hardware limitations that prevent access to physical disk storage
media as a result of size limitations.

      In personal computer operations, when available disk media is
not large enough to support required system activities, but more than
one drive is available, a method of transparently combining the disks
to appear as a single larger disk can solve this problem.  In order
to be transparent, there are two requirements:  a) The operating
system must be able to access the multiple media in exactly the same
way that it accesses a single disk and b) The disk controller must
access the multiple media in exactly the same way that it would
access multiple media.  In essence, the operating system must think
there is one disk, but when the hardware is accessed it must be
accessed as if multiple media is present.  The concept described
herein performs the required operations using the interface code
between the operating system and the hardware Basic Input Output
System (BIOS) or Machine Interface Layer (MIL).

      The key to the implementation is the ability to locate a
special machine readable label on each disk medium.  On the magnetic
rotating disk media, this involves dedicated fields within dedicated
sectors on the disk.

      On Solid State File (SSF) media, the concept involves special
blocks of memory outside of those used for standard system storage.
Hardware must be provided for reading and writing this special block.
When this key location for the labeling has been established, the
next step is to select a unique identity (ID) number for the combined
set.  The ID number can be very simple if the media is fixed within
the system.  The ID could be a zero if there was only a single set
and fixed in the system.  If there are multiple sets in the system
but are fixed, the IDs for each set can be simple sequential
integers.

      In removable disk media, the ID must be an approximation of a
universally unique ID.  The ID number for a particular set of
combined disks must have a low probability of coming into close
proximity of another combined set with the same ID number.  To insure
against such cases, a pseudo-randomly generated ID number of at least
thirty-two bits is considered sufficient.

      The labels used must include the ID number as described a...