Browse Prior Art Database

Use of Non-Volatile Semiconductor Storage for Disk Array Parity

IP.com Disclosure Number: IPCOM000102460D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 38K

Publishing Venue

IBM

Related People

Bennett, BT: AUTHOR [+2]

Abstract

Disclosed is the concept of using non-volatile semiconductor storage to maintain redundant data for an array of disks, instead of on a disk as described in (*). The redundant data is used to reconstruct data lost in the event of an otherwise unrecoverable disk failure.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 84% of the total text.

Use of Non-Volatile Semiconductor Storage for Disk Array Parity

       Disclosed is the concept of using non-volatile
semiconductor storage to maintain redundant data for an array of
disks, instead of on a disk as described in (*). The redundant data
is used to reconstruct data lost in the event of an otherwise
unrecoverable disk failure.

      A typical use of the concept involves sectored disks in which
each sector may be read or written individually.  The non-volatile
store is also divided into sectors with bit j of sector i being the
parity bit for bit j of sector i of each of the disks. If a
sector from one of the disks is lost, it can be reconstructed as each
bit is simply the parity bit for the bits in that position on the
other disks and the non-volatile store.  When an individual disk
sector is written, then the parity sector on the non-volatile store
can be updated using the old parity and old data.
      New parity =(old data XOR new data) XOR old parity

      Sectors on disk and in non-volatile store may also contain
redundant data so that many errors can be handled locally. The
non-volatile store could be resident with the disks and a local
controller could handle the update of the store or it could be part
of an overall system-managed store. In that case the system controls
the assignment of disk sectors to the sectors of users' files. A user
could specify the maximum degree of sharing parity for his file. The
smaller the number the less...