Browse Prior Art Database

Handling Data Integrity Exposures When Updating Erasable Optical Media

IP.com Disclosure Number: IPCOM000121900D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Burke, WT: AUTHOR [+4]

Abstract

Many of the current erasable optical drives on the market make updates the following way: * Pass 1: Erase sectors which are about to be updated. * Pass 2: Write the new or updated information to the sectors. * Pass 3: Verify the updated sectors were written correctly.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 60% of the total text.

Handling Data Integrity Exposures When Updating Erasable Optical Media

      Many of the current erasable optical drives on the market
make updates the following way:
  *  Pass 1: Erase sectors which are about to be updated.
  *  Pass 2: Write the new or updated information to the sectors.
  *  Pass 3: Verify the updated sectors were written correctly.

      Should there be a power failure during the "erase pass" (Pass
1), the data which previously existed on the sectors being updated
would be lost.

      This is a significant problem since the data in the sectors
being updated may be critical. In the case of directories on the
media (pointers to other data), multiple entries may be in the same
sector.  An update to a given entry would expose entries which are
not currently being updated. This is unacceptable in many
environments.

      This article describes a technique which avoids this problem
without a performance penalty at the expense of media usage.

      The technique involves allocating two sectors for every sector
which is deemed critical. At any one time, one sector would contain
the good data and the other sector would be erased. When an update is
required, the data would be written to the erased sector, verified,
and then the sector which contains the old data would be erased. The
data management system program would be aware of which sector
contained the data and which sector was erased.

      In the event of a failure durin...