Re: determine needed disk arms when replacing old disks

J Franz <franz400@xxxxxxx> wrote on Mon, 10 Feb 2014 17:33:33
GMT:

We currently have 42 disks, and they vary from 4327's (52Gb,
61Gb, 70Gb) and 4328's (105Gb and 141Gb). We need to double
current 3.2Tb (2 partition - 705Gb and 2.5Tb) I would think we
don't need 42 new SAS drives.

It's obvious from the mention of different drive sizes that
you're using RAID5 today. If you want to stay with RAID5,
you'll end up more than doubling your TBs because the smallest
SAS drive available is 139.5 GBs.

4327s & 4328s are 15K RPM drives. New SAS drives are either 15K
or 10K .... Let's just stick with 15K drives. There is a tiny
0.2ms performance gain going from 15K 3.5" drives to 15K 2.5"
drives. SAS versus SCSI is not really part of the equation.
But I've recommended with success reducing the quantity of
drives by 10% just due to this technology change.

Changing over to newer SAS adapters may lead to further
reductions, but you didn't mention your existing adapter
technology nor the drives per LPAR.

Jim's right, you might be able to create a i host LPAR which can
then virtualize all the storage to other i LPARs. Or you could
go with a V3700 and 4 fibre channel adapters ... no VIOS
required.

If you really want to get scientific about your needs, you can
use Performance Data Investigator to send your performance data
to Workload Estimator and play some configuration "what if"
games.