In RAID 6, the parity blocks are stored in duplicate, this is called double parity. In this RAID level, data blocks can still be written and read from the virtual disk array even if two disk errors occur at the same time or several hard disks fail.
In RAID 7, a separate computer is responsible for disk management. Both RAID systems increase fail-safety by combining the systems described. RAID 7 is used as a local real-time operating system in the RAID controller.