RAID 6, also called as double-parity redundant array of independent disk, uses two parity stripes on each disk. It supports for two disk failures within the RAID set before any data is lost.
RAID 6 configuration provides very high level of fault and drive failure tolerance. It is commonly used for environments which require long data retention periods, such as, for instance – archiving. One main disadvantage associated with this configuration is that each set of parities must be calculated separately, that slows down write performance. Implementing RAID 6 configuration is also more complex as it has to calculate two parity data for each data block, and expensive because two extra disks required for parity.
Similar to RAID 5, RAID 6 array does block level striping. Although, it uses dual parity. It creates two parity blocks for each data block, and can handle two disk failure.