OpenEye G4 GraniteRack - Manual (Page 26)

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RAID 3 sector-stripes data across groups of drives, but one drive in the group is dedicated to storing
parity information. RAID 3 relies on the embedded ECC in each sector for error detection. IN the case 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 fro 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.