What is RAID?

RAID (redundant array of independent disks or redundant array of inexpensive disks) is a data storage technology that combines multiple disks in a single logical volume in order to achieve greater protection against hardware failures, greater performance or a combination of both.

Common RAID schemes are RAID 1 – also known as mirroring – and RAID 5.

There’s a complete list of all RAID schemes on Wikipedia.