Asus PCI-DA2200 - Manual (Page 273)

ASUS GUI RAID Manager: Array Management
4-22 4.9 Assigning Spare Drives
3. Select Delete.
4.9 Assigning Spare Drives
You can assign spare drives to a logical drive to serve as backups
for failed drives. In the event of a drive failure, the spare drive
will be automatically configured into the array and
reconstruction (or rebuilding) will immediately commence.
Logical drives can support multiple spare drives; this
configuration however is rarely used due to its high cost and
uncommon occurrences of drive failures. A practical
configuration calls for one spare drive per logical drive
−
after
rebuilding on this drive, just replace the failed drive and then
configure the replacement as the new spare drive of the logical
drive.