Figure 1. Device parity set with failed disk unit.
Some examples show what happens to write operations when a single disk unit fails in a device parity set with device parity protection. The following figure shows a failed unit under an IOA with device parity protection.
It shows a parity set with four disk units. Each section of the disk unit is marked with a number. Parity sectors are noted with a p. Disk unit 3 is failed. Disk unit 1 shows sectors 1, 2, 3, and 4p. Disk unit 2 shows sectors 4, 1, 2, and 3p. Failed disk unit 3 shows sectors 3, 4, 1, and 2p. Disk unit 4 shows sectors 2, 3, 4, and 1p.
Note: RAID 6 operations are derived from RAID 5, but at a further
level of complexity. Because the concept is similar to RAID 5, RAID 6 operations
are not described here.