Setting Up a Spare Drive
You can set aside an unassigned drive as a global spare. Then, if any disk in a RAID set
fails, the spare is automatically integrated into the set to take the place of the failed
disk. Only RAID 1, RAID 0+1, and RAID 5 sets can take advantage of spare drives.
To set up a spare drive:
Open RAID Utility.
Select the drive you want to use as a spare in the left column.
Choose RAID > Make Spare.
You can also assign unused drives as spares by selecting the “Use unassigned drives as
spares” option when you create a set using the Create RAID Set command.