Abstract: A RAID system includes a pair of RAID controllers adapted to operate in active-active mode, each controller including a cache memory and at least one SAS/SATA I/O chip connected to a plurality of hard disk drives. Each SAS/SATA I/O chip includes more SAS/SATA ports than required to carry data to the hard drives. The caches in the respective controllers are synchronized via the extra SAS/SATA ports in each controller.

Abstract: A two-dimensional parity method and system that provides three-disk fault tolerance in an array of disks, such as a RAID system, is presented. The method includes arranging strips containing data in the disk array into horizontal and diagonal parity sets, each parity set including at least one data strip as a member and no single data strip is repeated in any one parity set. The diagonal parity sets are then grouped into two groups of diagonal parity sets—Group 1 and Group 2—such that each data strip is a member of a unique diagonal parity set in Group 1 and a unique diagonal parity set in Group 2. Horizontal XOR parities are calculated and stored in a designated disk. Diagonal XOR parities are calculated and at least some of the diagonal XOR parities are stored in a designated disk. The remaining diagonal parities are stored in a diagonal parity stripe so that diagonal parity can be retrieved in the event of a disk failure.