A data storage system having a pair of CPU modules each one of having a port coupled to a host computer/server and a storage medium for transferring data during an IO transfer. Each one of the modules produces different types of reset signals, one of such types being a software reset signal produced during a software upgrade of the module and other types being produced for events other than during a software upgrade, The other types produced by a first one of the modules disables the port of the first one of the modules; whereas, in response the software reset signal produced by the first one of the modules during an IO transfer, a second one of the modules couples the port of the first one of the modules to the second one of the modules to enable the IO transfer to be processed by the second one of the modules.