A mirrored volume is a hard drive or other form of storage media that stores an ...

A fault-tolerant volume that duplicates data on two physical disks. It provides data redundancy by using a copy (mirror) of the volume to duplicate the information contained in the volume. The mirror is located on a different disk. If one of the physical disks fails, the data on the failed disk becomes unavailable, but the system continues to operate using the unaffected disk. A mirrored volume is slower than a RAID-5 volume in read operations but faster in write operations. You can create mirrored volumes only on dynamic disks. You cannot extend mirrored volumes. In Windows NT 4.0 Disk Administrator, a mirrored volume is known as a mirror set. See also Dynamic disk, Dynamic volume, Fault tolerance, RAID, Volume.

a fault-tolerant volume duplicating your data on two physical hard disks