I recently moved the 36G TSM database and 10G log from attached SCSI disk
drives to a SAN. Backing the db now takes twice as long as it used to
(from 40 minutes to 90 minutes).  The old
attached disk drives are non-RAID and TSM mirrored.  The SAN drives are
RAID-5 and TSM mirrored.  I know I have to pay a penalty for writing to
RAID-5.  But considering the massive cache of the SAN it should not be
too bad.  In fact, performance of client backups hasn't suffered.

However, the day after the move, I noticed that backup db ran for twice
as long.  It just doesn't make sense it will take a 100% performance hit
from reading from RAID-5 disks.  Our performance guys looked at the sar
data and didn't find any bottlenecks, no excessive iowait, paging, etc.
The solution is to move the db and log
back to where they were.  But now management says: "We purchased this
very expensive 2T IBM SAN and you are saying that you can't use it."
Meanwhile, our Oracle people happily report that they are seeing
the performance of their applications enjoy a 10% increase.

Has anyone put their db and log on a SAN and what is your experience?
I have called it in to Tivoli support but has yet to get a callback.
Has anyone noticed that support is now very non-responsive?

server; AIX 4.3.3,  TSM 4.2.1.15

Thanks,
Eliza Lau
Virginia Tech Computing Center
1700 Pratt Drive
Blacksburg, VA 24060
lau AT vt DOT edu