7.8. RAID 3-Parity Check

7.8. RAID 3 Parity Check

RAID 3 leverages the basic organization of RAID 0, but adds an additional disk to the stripe width to hold the parity data. Like RAID 0, RAID 3 divides the data into stripes and the parity disk contains corresponding blocks that contain the computed parity for the data blocks on each member of the stripe unit, as shown in Figure 7-8.

Figure 7-8. Effects of RAID 3 on performance.

RAID 3 handles large quantities of sequential I/O at a relatively low cost. Bulk I/O is normally requested in large increments and RAID 3 performance is maximized for sequential I/O. RAID 3 has been popular in the supercomputing arena.

However, RAID 3 does not work well for random access I/O, including most database management system workloads. Random access suffers under RAID 3 because of the physical organization of a RAID 3 stripe every write to a RAID 3 volume involves accessing the parity disk. RAID 3 uses only one parity disk and it becomes the bottleneck for the entire volume.

Note

HP does not support RAID 3, because the clock circuit synchronizes the platter/spindles and because each drive is on a dedicated bus to the controller (multiple chips, one per SCSI bus).