Browse Prior Art Database

Salvage Operation for Otherwise Unreadable Sectors

IP.com Disclosure Number: IPCOM000110545D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 4 page(s) / 172K

Publishing Venue

IBM

Related People

Beglin, TW: AUTHOR [+4]

Abstract

This article describes a method to recover the user data in an otherwise unreadable sector on a Laser Magnetic Storage International (LMSI) 12-inch optical disk medium by using the Salvage Data command when the LMSI LaserDrive* 1250E optical disk drive reports an unable to read data error condition.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 39% of the total text.

Salvage Operation for Otherwise Unreadable Sectors

       This article describes a method to recover the user data
in an otherwise unreadable sector on a Laser Magnetic Storage
International (LMSI) 12-inch optical disk medium by using the Salvage
Data command when the LMSI LaserDrive* 1250E optical disk drive
reports an unable to read data error condition.

      The IBM 9246/9247 RPQ Optical Storage Subsystem Products
consist of a FileNet** Optical Storage and Retrieval (OSAR**) 64
model 100 optical disk library with two or four LMSI LaserDrive 1250
Enhanced digital optical disk drives.  The LMSI LaserDrive 1250E
optical disk drive supports 12-inch double-sided write once read many
(WORM) optical disk media.  The media has a storage capacity of 1
gigabyte per side, for a total capacity of 2 gigabytes per optical
disk.  The FileNet OSAR  64 optical disk library has a capacity of 64
12-inch optical disk cartridges for a total storage capacity of 128
gigabytes.

      The LMSI 12-inch optical media contains 1,024,000 sectors
arranged in a spiral groove on each side of the disk.  Each sector
contains 1200 bytes of raw data of which 1025 bytes is reserved for
user data.  The sector is divided into two parts:  a 15-byte
pre-recorded header followed by a 1185-byte data field.  The 15-byte
pre-recorded header followed by a 1185-byte data field.  The 15-byte
header contains the individual fields shown in Fig. 1.  The 1185-byte
data field contains the individual fields shown in Fig. 2.

      The vector address consists of 6 bytes of data followed by 20
bytes of ECC parity check symbols.  The information in the vector
address field is inserted by the LMSI LaserDrive 1250E optical disk
drive as each sector is written and is used during read operations to
monitor for sectors that were flagged as defective when written.  The
vector address for a user data field is written in the sector
physically following (i + 1) the sector containing the user data (i).
It acts as a pointer to inform the integrated optical controller as
to whether or not the particular user data field should be released
to the requester as valid data during a read operation.  If the LMSI
LaserDrive 1250E optical disk drive is unable to read a particular
sector and reports the problem to the requester, the problem could be
either a bad vector address field or bad User Data Field.

      The LMSI LaserDrive 1250E optical disk drive performs a process
called Direct Read During Write (DRDW) while writing the data.
Essentially, the read gate is opened during the decay of the write
pulse of the laser and the trailing edge of the written bit can be
detected and verified.  This operation enables the LMSI LaserDrive
1250E optical disk drive to eliminate a subsequent verify pass over
the written sectors in order to verify that the sectors were properly
recorded.

      If sector i is verified as good, then the appropriate vector
address is recorded in the s...