Abstract: The RAID system disclosed here uses arbitrated fiber channels or switch fabric to connect multiple host computers and storage array controllers (SAC). Each SAC is designated a primary SAC for an array of storage units, which it normally serves as controller, and as a secondary SAC for another array of storage units. A primary SAC, secondary SAC, and array of storage units is termed a storage unit set. When the primary SAC or associated host computer fails, the failure is detected by an interface chip, which causes the secondary SAC to assume the identify of the primary controller. Using system configuration information from the DASDs, the secondary SAC then controls the storage units of the storage unit set along with the storage units of which it is primary SAC. With this configuration, there is no need for switch apparatus between the storage arrays and there is no interference because dual ported storage units are used.

Abstract: In order to provide redundancy of host computers and storage array controllers, and thereby protect operation of a RAID system against host computer or storage array controller failure, two single RAID subsystems are conventionally provided in a conventional active-active configuration. This means each storage array controller has electrical access to each disk in its array as well as each disk in the other controller's array. The resultant interference between the controllers in accessing the disk channels causes the active-active system to normally function at approximately 130% of the speed of a single RAID system, rather than the optimum 200% of the speed of a single RAID system. The system of this invention, FULL-SPEED ACTIVE-ACTIVE redundant RAID system, contains a normally open switch or repeater which allows access by each storage array controller only to that controller's array of disks when both host computers and storage array controllers are operating normally.