Is there any advantage in creating multiple LUNs from a SAN to an AIX
host for stgpool volumes?

I have created a single large LUN on our SAN and put a bunch of backuppool
volumes within the filesystem.

As the system is growing I'm finding the need to do some tuning (as things
are not as springy as they once were). I'm seeing a lot more Wait I/Os and
things like migrations have definately slowed down.

It got pointed out to me by a friend who said it was better to create
a bunch of smaller LUNs, as it spread the load on the Storage array end
(fair enough). But he also said it slowed the system down due to volume level
write locking.

I didn't think modern Unix systems used volume level write locking
(understandable of the physical disk write constriction, but not from the
OS level)

The storage array in question is a Shark, I created the LUN from a complete
rank (200GB). The peak disk throughput from the TSM system is around 30MB/sec.
When the tape drives are firing to each other, it can almost be double on the
HBA.
The Shark gets hit more during the day from a bunch of DB servers, plus it's
only 1.6TB populated. The last time we had the ESS expert running, there was
95% read and 100% write to cache. The load hasn't significantly increased.

Any filesystem experts willing to share their opinion?

Cheers, Suad
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