Well Jonathan,

This is how we do it.
We are running on an AIX box for starters.
We have our 4 DB volumes on an separate filesystem. This is about 40GB in
total having 20 GB extendable. We do not mirror the DB volumes, because the
ESS provides all the redundancy we could need. No pain in case of disk
crashes. No management burden. Leaves more resources to TSM. Our database
has a 50% mutation daily, but we manage to keep up a 98% to 99% cache hit
ratio. This high mutation level made us decide to do a full DB backup twice
a day. We also do a daily reset of all the utilization values.

All our disk storage pool volumes also are on the same ESS, but in different
filesystems. These total to about 900 GB.

We have 2 fibre channel connections directly attached to the ESS. No SAN
yet. Both FC connections are based on redundancy and load-balancing using
IBM's subsystem device driver (shipped with the ESS). The ESS disks look the
same as local disks to an AIX box, so we simply put the ESS disks in AIX
volume groups/logical volumes/file systems.

Assumingin you know something about the ESS:
Inside the ESS whe have defined our 4 (DB) disks on 4 different loops (2
ranks or 8 packs) so we have 2 hot-spare disks available for each DB volume.
This also provides the best possible performance.


So Jonathan. Put your primary DB volumes on an ESS, and you don't need any
mirrors.
Let us know what you decide to do. Have fun.

greetings,

Ilja Coolen.