Abstract: A method and means for coding an (M-1).times.M data array written onto an array of M synchronous recording paths and for rebuilding and writing onto spare recording path capacity when up to a preselected number R of array DASDs fail, or one DASD becomes erroneous and up to R-2 fail. Data is mapped into the parallel paths using an (M-1).times.M data and parity block array as the storage model where M is a prime number and each block extent is uniform and at least one bit in length. The (M-1).times.M data and parity block array is encoded to include zero XOR sums along a traverses of slopes 0, 1, 2, . . . , P-1, extended cyclically over said data array. Rebuilding data and parity blocks is occasioned upon unavailability of no more than R less than or equal to P recording path failures, or one recording path in error and up to R-2 recording path failures.