RAID Level 1

A redundant Redundant Array of Independent Disks (RAID) level in which identical copies of data are maintained on pairs of disk drives, also known as mirrored pairs. RAID Level 1 uses disk mirroring to make an exact copy from one disk drive to another disk drive.

RAID Level 1 offers the best data availability, but only half of the disk drives in the array are available for user data. If a single disk drive fails in a RAID Level 1 array, all associated logical drives become degraded, but the mirrored disk drive allows access to the data. RAID Level 1 can survive multiple disk drive failures as long as no more than one failure exists per mirrored pair. If a disk drive pair fails in a RAID Level 1 array, all associated logical drives fail, and all data is lost.