a redundant array storage system including storage units divided into two logical arrays . the redundant array storage system further includes a plurality of array control units which are all fully utilized to control data transfers between the logical arrays and a central processing unit , each controller being capable of taking over the task of a failed controller . in normal operation , each redundant array controller may only access data stored in a logical array assigned to that controller . if the other redundant array controller fails , the remaining controller may access the data stored in the logical array assigned to the failed controller only through a secondary control process that is independent from the primary control process of the remaining controller . thus , the invention prevents parity data associated with user data placed in storage from being corrupted by attempts of two or more array control units to access the same redundancy group of data concurrently .