RAID 1, also known as disk mirroring, is a level of RAID in which data is duplicated on both disks of an array. RAID 1 requires two disk volumes in the array. With RAID 1, each disk is a mirror of the other disk. Because disks are mirrored, there will need to be an even amount of disks within the array.

The capacity of the RAID volume is half the total sum of the disks within the array. For example, if there are two 4TB disk drives in a RAID 1 array, that volume can only be as large as 4TB.

Advantages of RAID 1

The advantage that RAID 1 has over standard disks is a continued use of the array even if one disk fails. Also, read speeds can equal the sum of each disks performance.

Disadvantages of RAID 1

With RAID 1 each disk must be the same disk size. If one disk is larger than the other, the larger disk will only be able to create a volume the size of the smallest disk. Because data is mirrored on the two disks, write speed is limited to the slowest disks write speed.