RE: Performance Impact of going from 2 parity drives to 4 paritydrivesin a 4-disk RAID set

You don't, the software on the raid controller controls it. I just gave
a for instance! But a three drive raid set only strips two drives.
That can be checked by looking at the drive model / formatted size. for
instance a 35G drive with striping show up considerable less than 35G.
Adding a 4th drive does not add any striping. So the two drives that
are striped will have a much heavier workload.

My example was only theoretical.

Here you can see same drive type with different sizes. They are all in
some sort of raid 5 set.


Size % I/O Request Read Write Read Write
%
Unit Type (M) Used Rqs Size (K) Rqs Rqs (K) (K)
Busy
1 6718 15355 77.0 .0 .0 .0 .0 .0 .0
0
2 4326 26373 77.0 .0 .0 .0 .0 .0 .0
0
3 4326 26373 77.0 .0 .0 .0 .0 .0 .0
0
4 4326 26373 77.0 .0 .0 .0 .0 .0 .0
0
5 4326 26373 77.0 .0 .0 .0 .0 .0 .0
0
27 6718 15355 77.0 .0 .0 .0 .0 .0 .0
0
28 6718 15355 77.0 .0 .0 .0 .0 .0 .0
0
29 6718 15355 77.0 .0 .0 .0 .0 .0 .0
0
30 6718 15355 77.0 .0 .0 .0 .0 .0 .0
0
31 6718 13161 77.0 .0 .0 .0 .0 .0 .0
0
32 6718 13161 77.3 .0 .0 .0 .0 .0 .0
0
33 6718 13161 77.1 .0 .0 .0 .0 .0 .0
0
34 6718 15355 77.0 .0 .0 .0 .0 .0 .0
0

More...



Chris Bipes
Director of Information Services
CrossCheck, Inc.


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Raul A. Jager W.
Sent: Thursday, August 21, 2008 3:02 PM
To: Midrange Systems Technical Discussion
Subject: Re: Performance Impact of going from 2 parity drives to 4
paritydrivesin a 4-disk RAID set

How do you control which drives have the parity? I had the idea that
the data and the parity are spread over all the disks in the RAID set.