Browse Prior Art Database

Multiple Copy Disk Storage Device Using 180o Synchronization Control

IP.com Disclosure Number: IPCOM000099401D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Document File: 3 page(s) / 122K

Publishing Venue

IBM

Related People

Dishon, Y: AUTHOR

Abstract

A technique is described whereby the operational performance of multiple copy disk storage operation is improved through the use of a 180o synchronization and monitoring control mechanism. The concept enables a pair of disk storage devices to operate 180o out of phase with each other, such that it is possible to access the disks concurrently and to access one of the disks after 90o latency, on average. Also discussed is an extension for a duplex system with synchronized disks.

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

Multiple Copy Disk Storage Device Using 180o Synchronization Control

       A technique is described whereby the operational
performance of multiple copy disk storage operation is improved
through the use of a 180o synchronization and monitoring control
mechanism.  The concept enables a pair of disk storage devices to
operate 180o out of phase with each other, such that it is possible
to access the disks concurrently and to access one of the disks after
90o latency, on average.  Also discussed is an extension for a duplex
system with synchronized disks.

      The synchronization of disk storage devices has been previously
proposed, whereby two copies of data are written concurrently on two
independent disk storage devices, so as increase performance through
greater bandwidth.  When utilizing synchronized disks, there are
generally more read than write operations.  Therefore, it is
advantageous to synchronize the independent disk storage devices to
assure that the disks are mirror images of each other.

      The synchronization of disks assures that the writing onto a
pair of disks is accomplished concurrently.  It utilizes one control
unit with the required interfaces and buffers.  In prior art, the
disks themselves were synchronized at 0o with each other, using
pre-recorded servo information pulses and an external reference
clock. This allowed comparison of the actual disk position with a
standard.  Motors of the disk were either accelerated or decelerated
to conform to a predetermined rotational velocity and position within
an acceptable tolerance.  Two copies of data were then written
concurrently on two independent disk storage devices.

      The concept described herein improves on the past proposals by
rotating the disks 180o out of phase with each other.  By accessing
both disks concurrently over two interfaces controlled by one control
unit, it is then possible to select that disk whose specified sector
will rotate under the read/write head first.  Therefore, the average
latency will be 90o, as compared to 180o in disks synchronized at 0o,
or if no method of synchronization is used.

      During a read operation, the disk whose latency is the smallest
of the two is selected for data transfer to the channel.  The other
disk, whose latency is 180o later is ignored, or aborted.  If the
read to write ratio is sufficiently large, say 4:1 which is typical,
the overall performance will be improved, due to the reduced latency.
This effect is counterbalanced by the write operation.

      During the write operation, three variations are possible.  In
all of the variations, both disks are acce...