It's a form of redundancy for hard drives. Basically, you have two exact same drives and the data is written to both drives. If one fails, you have a "mirror" of it as a backup.
Aka: RAID 0.
RAID: Redundant Array of Inexpensive Disks (an old term - disks used to be VERY expensive).
Aka: RAID 0.
RAID: Redundant Array of Inexpensive Disks (an old term - disks used to be VERY expensive).