Raid 5 is nice because it allows you to lose one disk without losing data. Two disks you lose everything. UNLESS, you have a hot spare. Then you can lose an extra disk for each hot spare and not lose data.

I have two 14 drive arrays (73GB each drive). I have one hot spare. I can lose two drives and not have a problem. If I lose three, my backups had better be good.

As already said, hot spare means you can swap out drives while the power is on.

So, I a drive and the hot spare takes over. It gets built from the 'parity' markers on the rest of the drives.

Now I replace the broken drive, while the power is still on and everything is running. Depending upon the software, the new drive will either become the hot spare OR the hot spare will copy it's information over to the new drive and revert back to a hot spare.

I've used both setups.

Is this a DBA job? Well that depends. I work VERY closely with my system admin. When the drives fail, I am usually the one that goes ahead and calls tech support to order new ones and I'm the one that does the installation. It's not 'really' my job, but I can help out the SA by doing it.

-SQLBill