RAID 6 uses two independent parity schemes that are distributed across the drives. It requires at least four drives versus a minimum of three drives for RAID 5. Since two parity schemes must be computed the contrioller overhead is greater than that of RAID 5. RAID 5 can suffer one drive failure and RAID 6 can suffer multiple drive failures depending on the number of drives in the array. RAID 6 is implemented through hardware (drive controller), whereas RAID 5 can be either software or hardware. RAID 6 is used in Faile and Application Servers, Database Servers, etc. As always you should backup your data and not depend on RAID.