On RAID levels are supported:
RAID 0: Striping = The sectors are alternately distributed between the two plates. This results in a higher data throughput rate and lower latency. Caution: This mode contains no redundancy! The probability of default is thus even higher than that of a single disk.
RAID 1: Mirroring = The two plates were not mirrored. If one disk, then it does not matter, you can work directly on, then only without the double safety. You have to replace the defective disk of the same type then only. Disadvantage: It has only the capacity of one disk.