Advantages
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

Disadvantages
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

RAID 6

Independent Data Disks with Two Independent Distributed Parity Schemes

Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads.RAID Level 5 requires a minimum of 3 drives to implement.