Hi Steve,
Okay. You trust SATA drives? I've been leary of them for a production database. Pardon my ignorance, but what is a "battery backed cache"? I know the drives have a built-in cache but I don't if that's the same. Are the 12 drives internal or an external chasis? Could you point me to a place that this configuration exist?
Get 12 or 16 x 74GB Western Digital Raptor S-ATA drives, one 3ware 9500S-12 or two 3ware 9500S-8 raid controllers with a battery backup unit (in case of power loss the controller saves unflushed data), a decent tyan board for the existing dual xeon with 2 pci-x slots and a matching 3U case for 12 drives (12 drives internal).
Here in Germany chassis by Chenbro are quite popular, a matching one for your needs would be the chenbro RM312 or RM414 (http://61.30.15.60/product/product_preview.php?pid=90 and http://61.30.15.60/product/product_preview.php?pid=95 respectively).
Take 6 or 10 drives for Raid 10 pgdata, 2-drive Raid 1 for Transaction logs (xlog), 2-drive Raid 1 for OS and Swap, and 2 spare disks.
That should give you about 250 mb/s reads and 70 mb/s sustained write rate with xfs.
Regards, Bjoern
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