Software RAID: RAID implementations done entirely in software, with no special hardware support
Hardware RAID: RAID implementations with special hardware
Use non-volatile RAM to record writes that are being executed
Beware: power failure during write can result in corrupted disk
E.g. failure after writing one block but before writing the second in a mirrored system
Such corrupted data must be detected when power is restored
Recovery from corruption is similar to recovery from failed disk
NV-RAM helps to efficiently detected potentially corrupted blocks
Otherwise all blocks of disk must be read and compared with mirror/parity block