What OS & service pack? Latest Linux & Windows will recognize the RAID & the hdds. In rare cases shall you need to make a RAID driver floppy.
That'd not be my concern. I would NOT trust the onboard RAID. I'd suggest you find a plan B in case the RAID fails. The safest way is to have an eSATA drive for storage/backups. You can just get a eSATA blanket into one of the expansion slot in the back of the case and hook up a eSATA enclosure with a large drive to it. Unless your case has a eSATA plug.