It is often the case that people are uncertain as to which type of RAID arrangement they are using. This can happen when they have bought an external storage device. They know that it is a RAID because there are multiple hard drives in it and the device shows itself as a single storage volume, they just don’t know what type. One of the ways that you can at least make an educated guess is by comparing the size of the volume offered by the device with the total capacity of the physical hard drives which the device uses.

The most common confusion regards external RAIDs with two hard drives (for example Lacie make a lot of these). Take the example of an external fitted with two x 1TB hard drives. If the storage space offered when you plug it into your computer shows 2TB then it is most likely a RAID 0 (or “striped”) configuration. If it shows 1TB then it is almost certainly a RAID1 (or “mirrored”) configuration.

To have a RAID 5 configuration you must have at least 3 physical hard drives. The capacity is equal to the total capacity of all of the drives minus 1 drive’s worth. This overhead is for the parity which allows it to survive the loss of a drive. Of course if a second drive subsequently fails then the skills of an experienced RAID 5 data recovery expert will be required.