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Re: Oracle Performance on RAID 5

From: Edward Whalen <ewhalen_at_perftuning.com>
Date: Thu, 11 Jun 1998 12:25:20 -0500
Message-ID: <35801300.3C98B57C@perftuning.com>


Robert
  With RAID 5 you will definately suffer on writes, but reads in general perform well on RAID 5. This has to do with how the parity is calculated and written to the drives. On a read, the controller simply reads the data off of the drive where it resides, therefore you can achieve the performance that you would expect from the number of drives that you have. For writes the parity is calculated by reading the data and parity stripes, computing the new parity and xoring in the new data and then writing them both back out. Thus, a logical write incurs 4 physical I/O's. In keeping with apx 70 random I/O's per second per disk drive you can see how your capacity can be reduced. Ed
--
Edward Whalen
President
Performance Tuning Corporation
Database Performance Consultants
Email: ewhalen_at_perftuning.com
Web: www.perftuning.com Received on Thu Jun 11 1998 - 12:25:20 CDT

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