Browse Prior Art Database

Dynamic DASD Array Protection for Failed Device Using Dual Copy

IP.com Disclosure Number: IPCOM000111145D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Ouchi, N: AUTHOR [+2]

Abstract

Disclosed is a method and means for accessing data from a DASD Array after a DASD device in a parity domain has failed. A domain is set of DASD devices over which a record or file has been segmented or striped and one of which stores the parity (XOR) of the segments. The prior art teaches that a spare DASD can be taken from a pool of spare DASD as a substitute for the failed device. The data on the failed device is reconstructed using the remaining devices and stored on the substitute device.

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Dynamic DASD Array Protection for Failed Device Using Dual Copy

      Disclosed is a method and means for accessing data from a DASD
Array after a DASD device in a parity domain has failed.  A domain is
set of DASD devices over which a record or file has been segmented or
striped and one of which stores the parity (XOR) of the segments.
The prior art teaches that a spare DASD can be taken from a pool of
spare DASD as a substitute for the failed device.  The data on the
failed device is reconstructed using the remaining devices and stored
on the substitute device.

      In this invention, data is protected until the failed device is
repaired or replaced.  The DASD Array consists of one or more parity
domains of N + 1 devices where the data are recorded for one or more
sets of devices as spare groups of N devices.  These are not parity
domains.  This is illustrated in Fig. 1a.  In the event of a device
failure in a parity domain, the remaining DASDs N are paired with N
DASDs in the spare group as DUAL, COPY, PAIRS.  This is illustrated
in Fig. 1b.

      As used, the data on the original device of the Dual Copy Pair
is copied on the spare device.  All update operations are written
onto both devices in the pair.  Data are read by using the data
reconstruction mechanism using N devices of either the original
parity domain or the devices in the spare group.  This protects the
data against the failure of a second device in that the data can be
reconstructed...