There are many different levels of
RAID. The implemented RAID level
depends on several factors, including overhead
of reading and writing data, overhead
of storing and maintaining parity,
plus the mean time to data loss (MTDL).
The most recent level is RAID 6, which
can have two implementations (Reed-
Solomon P+Q or Double Parity). RAID 6
is the first RAID level that allows the
simultaneous loss of two disks, which
improves its MTDL over RAID 5.