RAID 1
, also known as disk mirroring, is simply a pair of disk drives that store
duplicate data, but appear to the computer as a single drive. Although striping is
not used within a single mirrored drive pair, multiple RAID 1 arrays can be striped
together to create a single large array consisting of pairs of mirrored drives. All
writes must go to both drives of a mirrored pair so that the information on the
drives is kept identical. However, each individual drive can perform simultaneous,
independent read operations. Mirroring thus doubles the read performance of a
single non-mirrored drive and while the write performance is unchanged. RAID 1
delivers the best performance of any redundant array type. In addition, there is
less performance degradation during drive failure than in RAID 5 arrays.
