|
Are these SAS drives or SCSI drives? I may be wrong but SCSI drives did
their raid striping over 2, 4 or 8 drives, depending on how many drives
were in the raid set when you first fired it up. For example, if you
started out with a three drive raid set (YUCK!) you will only have your
striping over 2 drives, even though your current set may now have 8 drives
in it. This is why three drive raid sets suck; the striping is only over
two drives. You can often tell how many drives have the raid striping
when you do a WRKDSKSTS. The drives with the raid striping will have less
capacity, because the striping takes away from the capacity. Much like
the question a few weeks ago when the poster wondered how he had drives
with different capacity's in the same raid set.
So, you're planning on going from a raid stripe spread out over 8 drives
to a raid stripe spread out only over 4 drives when you drop down from 8
drives to 7. This could have performance implications. Won't be as bad
as dropping down to a 2 drive raid stripe! (Pass me the short sword
master.)
You may have to stop and restart raid to do all this, see? Don't lose a
drive during this.
SAS drives spread the raid striping over the number of drives initially in
there when you start raid. A three drive raid set should have the stripe
over three drives and not two. Now, if you add a drive the striping
should still stay just over the first drives. A SAS seven drive raid set
(with the 8th drive as a hot spare) should have the striping over all
seven drives.
I hope I am correct.
Rob Berendt
--
IBM Certified System Administrator - IBM i 6.1
Group Dekko
Dept 1600
Mail to: 2505 Dekko Drive
Garrett, IN 46738
Ship to: Dock 108
6928N 400E
Kendallville, IN 46755
http://www.dekko.com
From: Jeff Crosby <jlcrosby@xxxxxxxxxxxxxxxx>
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>,
Date: 09/24/2013 08:54 AM
Subject: Change Raid Settings
Sent by: midrange-l-bounces@xxxxxxxxxxxx
Yesterday we had a disk failure at 4:27pm, which happens to be 3 minutes
before we run our entire days business. Good timing, eh? We ran
everything and then replaced the drive and rebuilt the RAID. I honestly
don't remember the last time we had a disk failure before this.
Our System i 520 is on i 7.1 and has 16 drives in it. There are 2 RAID
sets with 8 drives each. Disk utilization is less than 19% so we have
plenty of space. (We used to have an IXS way back when, which is why
we're
way over capacity on disk.)
The service guy (ServIT) thought, since we're on 7.1, it might be possible
to change each of those 8-drive RAID sets to a 7-drive RAID set with a hot
spare. I questioned him because of the age of our hardware and said he
still thought it was possible. He's going to look into it today.
Since there are some very smart hardware people on this list, I'm going to
ask here. Can that be done? Can that be done without a reload?
Thanks.
--
Jeff Crosby
VP Information Systems
UniPro FoodService/Dilgard
P.O. Box 13369
Ft. Wayne, IN 46868-3369
260-422-7531
www.dilgardfoods.com
The opinions expressed are my own and not necessarily the opinion of my
company. Unless I say so.
--
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