8
Under
RAID 5
parity information is distributed across all the drives. Since there is no dedicated parity
drive, all drives contain data and read operations can be overlapped on every drive in the array. Write
operations will typically access one data drive and one parity drive. However, because different
records store their parity on different drives, write operations can usually be overlapped.
RAID 6
is similar to RAID 5 in that data protection is achieved by writing parity information to the
physical drives in the array. With RAID 6, however,
two
sets of parity data are used. These two sets
are different, and each set occupies a capacity equivalent to that of one of the constituent drives. The
main advantage of RAID 6 is High data availability – any two drives can fail without loss of critical data.
Dual-level RAID
achieves a balance between the increased data availability inherent in RAID 1 and
RAID 5 and the increased read performance inherent in disk striping (RAID 0). These arrays are
sometimes referred to as RAID 0+1 or RAID 10 and RAID 0+5 or RAID 50.