hi there... i'm relatively new to the world of Linux...and even more so to RAID... I'm about to install an Adaptec RAID card into a server running rhel4... the initial idea was to configure RAID5 on four 73G HD...although i'm thinking that i should probably do a RAID 5 on three HD and leave the last for for a possible hot swap if a HD fails? I've never done this before...ever...period....
So, RAID guru's and Linux guru's out there.... any pointers? tips? something to look out for?
Any comments, tips, ideas...anything at all is highly appreciated!
Thanks in advance... :-)

RAID 5 can survive one disk failing. The only reason to have hot spare is if you fear you're going to have a second disk fail before you physically replace the failed first disk and have it recover. The hot spare would allow it to rebuild the "failed" drive as soon as it failed. Usually however once you physically replace the failed drive then it rebuilds back to the new drive so that the hot spare can again become the hot spare.

For a small system that only had 4 drive bays unless it was mission critical AND space wasn't expected to ever be an issue I wouldn't bother with a hot spare. We do have high end disk arrays with 15 disks in each enclosure used for large (4 TB) databases. In those we do RAID 1/0 and we do reserve disks for hot spares. Once two years ago while we were doing RAID 5 we did see two disks fail in the same RAID group but overall this is a fairly rare kind of event.