A computer system having a work computer, first storage systems, and second storage systems also has a network, a network routing device, and a management computer. Upon receipt of the update data from the work computer, the first storage system stores the update data in a first storage volume and stores the update data in a second storage volume until the update data is transferred to the second storage system. The management computer obtains an used capacity of the second storage volume of each of the first storage systems and controls the routing of the data by the network routing device based on the obtained used capacity to prevent the cache of each of the storage systems from being overflown.