HP ProLiant Servers AIS: Official Study Guide and Desk Reference

7.9. RAID 4 Data Guarding

RAID 4 uses data striping in combination with a dedicated parity drive, as shown in Figure 7-9. Three or more disks are required for a RAID 4 disk set.

If one drive fails, data from the failed disk can be reconstructed from the other drives in the array. Because only one drive is used for storing checksums, available disk space is higher than with mirroring. The more disks there are in the logical drive, the better the performance, because all drives can be accessed individually. Several operations (even mixed read and write operations) can take place at the same time. RAID 4 stores parity information for each data stripe on a single disk. RAID 4 can tolerate only a single disk failure.

Note

RAID 4 drives can share the same bus.

Note

Because RAID 4 can tolerate the failure of one drive without losing data, it is considered fault tolerant. RAID 4 can support RAID memory.

7.9.1 RAID 4 Limitations

In write-intensive environments, the parity update operations are serialized to a single disk. Because every write operation requires that data be written to the parity disk, this disk can become a performance bottleneck. Consequently, the use of RAID 4 has rapidly declined.