I am no expert, but have been asking them a bunch and I think your missing a
key concept.
The data is best on several drives.
I could be completely off, but if I understood (I just finished doing the
same kind of thing minus several databases) you want your WAL on fast drives
in raid 1 and your data (as many drives as you can use) on raid 10 (can be
slower drives , but I saw you already have a bunch of 15k drives).
So you may get best performance just using one database rather then several
smaller ones on mirrored data drives. Keep in mind if you go with ES4 (I am
using AS4) and postgres 8 you can add spindles and move hard hit tables to
their own spindle.
Again I am no expert; just thought I would echo what I was informed.
I ended up using 2 15k drives in raid 1 for my WAL and 4 10k drives for my
data in raid 10. I ended up using links to these from the original install
of postgres on the raid 5, 4 15k drives inside the server itself. I believe
this gives me three separate raid arrays for my install with logs and such
on the raid 5, data on the raid 10 and wal on the raid 1. I am in the
testing and conversion phase and have found it very fast. I used a 4
processor Dell 6550, but think from what I have been told your computer
would have been a better choice (CPU wise). I am not using fibre but do have
a 14 drive powervault which I split to have the 15k's on one side and the
10k's on the other. So I am using both channels of the controller. I have
been told for me to get best performance I should add as many 10k drives to
my data array as I can (but this was all I had in my budget). I have room
for 3 more drives on that side of the powervault.
Best of luck on your project.
Joel