Appendix
RAID Level 2 is a stripe set that uses “Hamming encoding” information to provide redundancy. Hamming encoding is a method of error correction normally used in solid-state random access memory. Because RAID Level 2 requires additional array management software and because it is generally more costly to implement than other RAID Levels, this RAID level is not widely used.
This is a stripe set with a dedicated member that stores parity information. Parity information is data that permits the recalculation of missing data if any single drive member is lost. RAID Level 3 requires that disk members be synchronized to reduce rotational latency. RAID Level 3 also assumes that all members of the array can be written to simultaneously. Since these require special disk capabilities and special array management software, RAID Level 3 is not widely used.
This is also a stripe set with a dedicated parity device. As data moves to the members, parity information is calculated and written to the dedicated parity device. If any member of the set fails, parity information is used to recreate the missing member. If the parity device fails, parity information is recreated from the existing data. Depending on the nature of the I/O traffic, the RAID 4 parity member may be a “hot spot” and bottleneck for the application since parity must be written to that member with every I/O operation.