RE: Performance Impact of going from 2 parity drives to 4paritydrives in a 4-disk RAID set -- MIDRANGE-L

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Put it this way:
Write to disk 1 - stripe to disk 2-4
Write to disk 2 - stripe to disk 1,3-4
Write to disk 3 - stripe to disk 1-2,4
Write to disk 4 - stripe to disk 1-3
or
guessing that disk 2 and 3 hold the striping:
Write to disk 1 - stripe to disk 2-3
Write to disk 2 - stripe to disk 3
Write to disk 3 - stripe to disk 2
Write to disk 4 - stripe to disk 2-3

As you can see disk 2 and 3 get heavily hit while 1 and 4 may not.

Chris Bipes
Director of Information Services
CrossCheck, Inc.

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Charles Wilt
Sent: Thursday, August 21, 2008 2:05 PM
To: Midrange Systems Technical Discussion
Subject: Re: Performance Impact of going from 2 parity drives to
4paritydrives in a 4-disk RAID set

Chris,

To to be sure...

You are saying there's a performance improvement going from a 4-disk
RAID 5 that only uses 2 parity drives to a 4-disk RAID 5 that uses all
4 drives for parity.

That's what I expected, but IBM is telling us otherwise.

We've already made the move from 3-disk RAID 5 to 4-Disk RAID 5.

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