I'll share my experiences with primary TSM diskpool on SATA drives for the
list, since this subject is becoming more common lately.

Environment:
TSM 5.3.4.0, AIX 5300-04-03, 1 CPU 4GB RAM LPAR on a p570
2 HBAs for disk, 1 HBA for 2 LTO3 drives
Backup is roughly 650GB nightly and will more than double very soon
EMC Clariion CX500, Flare code 19, default cache settings - 8kb block
size, etc.
I originally had only 5 7200RPM 250GB SATA drives to work with
That has now changed where I'm spread across 10 drives

I first started by trying out RAID5 just to see what I could get.  Not
much.  Roughly 25MB/sec writes to a single 4+1 RAID5 array.

I next switched to a single 4+1 RAID3 array.  After some JFS2 tuning I
maxed out at 77MB/sec writes, 123MB/sec reads (migration).

I was able to go beyond my 5 SATA disks and use 5 others as well.
I went to 2 4+1 RAID3 arrays with a usable capacity of about 1823GB each.
I carved up one 900GB LUN on each array and assigned it to TSM.
Element size on each array was the default - 128 blocks, 64K
Each 900GB LUN is owned by a different SP on the CX500.

I experimented by creating a striped LV across both LUNs with various
stripe sizes and then used define vol diskpool xxxx formatsize=xxx to
create a diskpool volume.
I used topas to monitor disk performance.
Performance was rather equal until 8K or 4K stripe sizes, which resulted
in slightly lower performance.  I settled on a 64K stripe size for the
striped LV.

That resulted in the same 77MB/sec writes from each array for a total of
154MB/sec.  I imagine getting another 5 drives and using another array to
stripe across would be even better.  I'm not sure at what point the
SPs/subsystem would max out, but it was showing 60% utilization on one SP
while I was running at max - there are also some mirrorview volumes and
other production data on the fibre drives in this same CX500 so the entire
subsystem is not dedicated to TSM.

The plan was to use the remaining free space on those SATA arrays for
clone LUNs, but we have yet to see if that is really feasible.

If anyone has any other tuning tips I'd be happy to listen.



______________________________
John Monahan
Consultant Infrastructure Solutions
Computech Resources, Inc.
Office: 952-833-0930 ext 109
Cell: 952-221-6938
http://www.computechresources.com