The present invention provides a control method for a storage device controller system provided with a first storage device controller that is connected to first and second storage devices storing data in the CKD format and the FBA format, respectively, and that has first and second communications control means that receive data input/output requests from a mainframe computer and an open system computer, respectively, and a second storage device that is connected to a third storage device storing data in the CKD format and that has third communications means connected to the second communications means, wherein the first storage device controller transmits a command to the second storage device controller if a data read request received from the open system computer is for data stored on the third storage device, and transmits the data that are read out from the third storage device by the second storage device controller to the open system computer.