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Browse Prior Art Database

Increased DASD Array Performance by Grouping of Devices

IP.com Disclosure Number: IPCOM000115802D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Ouchi, NK: AUTHOR

Abstract

Disclosed is the ordering of devices by seek time performance and then selecting the RAID groups using devices of similar performance. The RAID group performance is still paced by the slowest device but now the devices are grouped with similar performance characteristics. While there will be faster groups and slower groups, the average across the population of RAID groups will approach the average of the individual devices. This is also illustrated in the Figure.

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Increased DASD Array Performance by Grouping of Devices

      Disclosed is the ordering of devices by seek time performance
and then selecting the RAID groups using devices of similar
performance.  The RAID group performance is still paced by the
slowest device but now the devices are grouped with similar
performance characteristics.  While there will be faster groups and
slower groups, the average across the population of RAID groups will
approach the average of the individual devices.  This is also
illustrated in the Figure.

      In a RAID 3 Array, the devices in a parity domain are accessed
in parallel.  Performance of the array is paced by the slowest
device.  Disclosed is the use of grouping devices of similar
performance to aid in improving the overall average performance of
multiple arrays.

      In a population of devices, the performance is spread due to
slight differences in electro- mechanical parameters.  If the devices
for the RAID parity groups are chosen in a random manner, the overall
performance of the RAID groups will be less than the average of the
device population due to the fact that each group is paced by the
slowest device in the group.  That is, all of the groups are slowed
by the random selection.  This is illustrated in the Figure.