RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by using a second independent distributed parity scheme (two-dimensional parity)

Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures

Perfect solution for mission critical applications

Very complex controller design

Controller overhead to compute parity addresses is extremely high

Very poor write performance

Requires N+2 drives to implement because of two-dimensional parity scheme