There are a loose coupling and a tight coupling as the coupling configurations for a first module and a second module. The loose coupling is a coupling configuration in which the first and second modules are coupled together by way of a front-end path, and the first module is not able to access a second storage resource. The tight coupling is a coupling configuration in which the first and second modules are coupled together by way of a back-end path, and the first module is able to access the second storage resource. A switch from the loose coupling to the tight coupling is performed using the following processing flow without the first and second modules being partitioned into respectively independent storage modules. Specifically, first, the first and second modules are coupled together by way of the back-end path, and next, the first module merges information denoted by second management information from the second storage resource with first management information via the back-end path.