Advice sought : new database server

I'd be grateful for advice on specifying the new server

We presently have one main database server which is performing well. As
our services expand we are thinking of bringing another database server
to work with it, and back each up via Postgres 9.1 streaming replication
each to a VM server -- at present we are doing pg_dumps twice a day and
using Postgres 8.4.

The existing server is a 2 x Quad core E5420 Xeon (2.5GHz) with 8GB of
RAM with an LSI battery-backed RAID 10 array of 4no 10K SCSI disks,
providing about 230GB of usable storage, 150GB of which is on an LV
providing reconfigurable space for the databases which are served off an
XFS formatted volume.

We presently have 90 databases using around 20GB of disk storage.
However the larger databases are approaching 1GB in size, so in a year I
imagine the disk requirement will have gone up to 40GB for the same
number of databases. The server also serves some web content.

Performance is generally good, although we have a few slow running
queries due to poor plpgsql design. We would get faster performance, I
believe, by providing more RAM. Sorry -- I should have some pg_bench
output to share here.

I believe our existing server together with the new server should be
able to serve 200--300 databases of our existing type, with around 100
databases on our existing server and perhaps 150 on the new one. After
that we would be looking to get a third database server.

I'm presently looking at the following kit:

1U chassis with 8 2.5" disk bays
2x Intel Xeon E5630 Quad-Core / 4x 2.53GHz / 12MB cache
8 channel Areca ARC-1880i (PCI Express x8 card)
presumably with BBU (can't see it listed at present)
2 x 300GB SAS 2.5" disks for operating system
(Possibly also 300GB SATA VelociRaptor/10K RPM/32MB cache
RAID 1
4 x 300GB SAS 2.5" storage disks
RAID 10
48.0GB DDR3 1333MHz registered ECC (12x 4.0GB modules)

My major question about this chassis, which is 1U, is that it only takes
2.5" disks, and presently the supplier does not show 15K SAS disk
options. Assuming that I can get the BBU for the Areca card, and that
15K SAS disks are available, I'd be grateful for comments on this
configuration.

Regards
Rory

--
Rory Campbell-Lange
rory(at)campbell-lange(dot)net

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