we have big forum , want upgrade to new server
current use 1 X 73GB 15k HDD
I want request new server

I want Fastest, best performance ,
we can request 2X 73GB 15k HDD
which is the best ?
use RAID or make one for db and other for php/html files ?
or 1 SCSI enough ? and make another for backup ?

if RAID which raid best for me?
and please tell me most important setting .