Fault tolerant transport mechanism in storage and method of controlling the same

A method of controlling a transport mechanism allows a first mobile carrier to move based on a power source incorporated in the first mobile carrier when an instructions signal specifying an access to a cell defined in a storage is supplied to a controller. When a fault is detected in the first mobile carrier, the first mobile carrier is moved based on the action of a second mobile carrier. The method ensures the movement of the first mobile carrier with the assistance of the second mobile carrier even when the first mobile carrier suffers from a fault. The first mobile carrier can be moved out of the movable range of the second mobile carrier. The second mobile carrier is allowed to move in the own movable range without an interference to the first mobile carrier. The second mobile carrier keeps operating without an interruption.