RAID 6 in some terms might be considered as improved version of RAID 5.It stripes blocks of data and parity across an array of drives the same as RAID 5, the only difference is that calculates two sets of parity information for each parcel of data. The idea of this duplication is to improve fault tolerance. RAID 6 can handle the failure of any two drives in array. Due to more calculation RAID 6 is considered to be slightly worse than RAID 5 in writing, but might be faster in random read operations. The same as in RAID 4 and 5 performance can be adjusted by setting different stripe size.

Controller Requirements: specialized hardware controller
Hard Disk Requirements: minimum of 4 hard drives, maximum is set by controller, all the discs should be the same size.
Array Capacity: size of the smallest drive*(number of drives -2)
Storage Efficiency: (number of drives -2)/number of drives
Fault tolerance: very good, loss of two drives can be tolerated
Availability: excellent
Degradation and rebuilding: degradation can be substantial after failure or during rebuild because of complexity of dual distributed parity
Random read performance: very good
Random write performance: poor because of dual parity overhead and complexity
Sequential read performance: good
Sequential write performance: fair good