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Preventing Data Loss on Power Off of Exposed Redundant Array of Independent Disks Box

IP.com Disclosure Number: IPCOM000114019D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Crews, CV: AUTHOR [+3]

Abstract

A non-volatile memory is installed in a Redundant Array of Independent Disks (RAID) box or, if a write cache is available, a part of it is used to store the entire write data and the entire parity update data until the write is completed. Therefore, if a drive which is part of the RAID box breaks and power is lost to the RAID box before the writes can be completed, the RAID can be properly updated without data loss once power is restored. This applies to writes begun before the drive breaks as well as to those begun after.

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Preventing Data Loss on Power Off of Exposed Redundant Array of Independent
Disks Box

      A non-volatile memory is installed in a Redundant Array of
Independent Disks (RAID) box or, if a write cache is available, a
part of it is used to store the entire write data and the entire
parity update data until the write is completed.  Therefore, if a
drive which is part of the RAID box breaks and power is lost to the
RAID box before the writes can be completed, the RAID can be properly
updated without data loss once power is restored.  This applies to
writes begun before the drive breaks as well as to those begun after.

      When one drive breaks in a RAID (Redundant Array of Independent
Disks), then the data for that drive must be recovered by exclusive
ORing the corresponding data blocks from the remaining drives in the
array.  Once the broken drive is replaced, then the data can be
rebuilt onto it.  Complete RAID protection is available once this
rebuild is complete.  The entire time that RAID protection is not
available is referred to as the Exposed state and the array is
referred to as an Exposed RAID array.

      When data blocks are being written to an Exposed RAID array,
both the data and the parity must be updated.  If power drops at any
time during this process the corresponding data on the broken drive
cannot be rebuilt because the data needed to rebuild it is lost
(parity is out of sync).  However, if a non-volatile memory is
installed or, if a...