Proware DP-503-F4A3, Installation And User Manual

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DP-503-F4A3 RAID SUBSYSTEM
Installation and User Manual 15
of drive failure, data recovery is accomplished by calculating the exclusive OR (XOR) of the
information recorded on the remaining drives. Records typically span all drives, which optimizes the
disk transfer rate. Because each I/O request accesses every drive in the array, RAID 3 arrays can
satisfy only one I/O request at a time. RAID 3 delivers the best performance for single-user, single-
tasking environments with long records. Synchronized-spindle drives are required for RAID 3 arrays in
order to avoid performance degradation with short records. RAID 5 arrays with small stripes can yield
similar performance to RAID 3 arrays.
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