RAID stands for Redundant Array of Independent Disks.
In simple terms, if you set your device to a RAID 0 (Stripe) then all the drives in the device are recognised as one large drive by the OS.
RAID 0 is generally used for speed, but provides no redundancy if one drive fails.
If you however set the device to a RAID 1 (Mirror) then you halve the total capacity of the device. While you have half the capacity, everything
you write to the first partition is automatically copied to the second partition. This is important as you will always have a safe backup of your data.
For further details on the different RAID configurations that exist, please see the following article :