Browse Prior Art Database

Method to Enhance Disk Reliability in Optical Libraries

IP.com Disclosure Number: IPCOM000105599D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 4 page(s) / 168K

Publishing Venue

IBM

Related People

Barnett, D: AUTHOR [+3]

Abstract

The invention disclosed here describes a method of increasing the reliable life of optical media residing in an Optical Information Storage Library. The media may be re-writable Magneto-Optical (MO) type or Write-Once-Read-Many (WORM) type. The invention described below does not affect the recording process on the MO or WORM disk. Rather, the method uses a software program that periodically checks the quality of the disk signal, and reassigns (writes) data to unused portions of the disk if the signal quality falls below an unacceptable limit.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 37% of the total text.

Method to Enhance Disk Reliability in Optical Libraries

      The invention disclosed here describes a method of increasing
the reliable life of optical media residing in an Optical Information
Storage Library.  The media may be re-writable Magneto-Optical (MO)
type or Write-Once-Read-Many (WORM) type.  The invention described
below does not affect the recording process on the MO or WORM disk.
Rather, the method uses a software program that periodically checks
the quality of the disk signal, and reassigns (writes) data to unused
portions of the disk if the signal quality falls below an
unacceptable limit.

      Optical MO/WORM media is subject to finite shelf life.  Disk
defects can grow in time to substantial sizes and can affect the read
signal within a sector.  Neighboring sectors in adjacent tracks are
also affected.  Under these conditions, customer data written on the
MO/WORM disk may become unreadable after an extended period of time.
Information Storage Libraries require that data be accessible for
any length of time.  Libraries using MO/WORM media are subject to
"data loss" conditions if the storage time requirements are
considerable.

      As of 2/90, various models of optical storage libraries which
use 5.25-inch rewriteable MO disks have been announced by the
following companies:  Cygnet, Hewlett Packard, Hitachi, Kodak, and
Mitsubishi.  Currently, IBM is also developing an optical library
product based on 5.25-inch MO technology.

      This invention disclosure describes a technique which can
significantly extend the reliable life and improve the data
reliability performance of MO/WORM media.  The disclosure is
intended for the IBM GPD Optical Storage Library Offerings, and
intended to achieve a substantial optical reliable life advantage
over that of the competitive offerings.

      The algorithm periodically reads in entirety each optical disk
in the library.  The procedure of testing the customer data, with
reallocation of degraded sectors, is called "refresh."  During the
refresh operation, all data sectors are read and checked with the
Error Correction Code (ECC-verified).  If an error threshold criteria
is not met during the ECC-verify of a sector, a read-verify operation
will take place for that sector.  Failing to pass the conditions for
read-verify will result in the physical movement of the data to
another part of the disk.  The sector re-assignment procedure must
guarantee the new location is acceptable.

      The refresh operation can be done in either 'off-line' or
'on-line' modes.  The off-line mode requires an idle drive with the
device address (MO/WORM disk) varied off-line.  This requirement
allows the continue servicing requests for alternate addresses.

      The on-line mode performs the refresh operation while the
device has system on-line status.  If the refresh is interrupted, the
key state parameters are saved in order to restart after the previous
request...