The M-Series appliances leverage RAID 1 for
data redundancy in the event of disk failure. Therefore, the pair
of drives in a RAID 1 array need to be identical. However, you are
free to mix drive capacities across different RAID 1 arrays. For example,
the drives in the A1/A2 RAID 1 array can be 1TB drives, and the
drives in the B1/B2 RAID 1 array can be 2TB drives.