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Definition of RAID Levels
RAID 0 is typically defined as a group of striped disk drives without parity or data
redundancy. RAID 0 arrays can be configured with large stripes for multi-user
environments or small stripes for single-user systems that access long sequential
records. RAID 0 arrays deliver the best data storage efficiency and performance of any
array type. The disadvantage is that if one drive in a RAID 0 array fails, the entire
array fails.
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.