A computer system dynamically assigns the storage capacity from pool volumes to the access target in the higher-level system, and can immediately respond to the change of the status of the pool having the pool volumes. The control device provides a plurality of first pools, provides a second pool, allocates a storage area from one of the first pools to a logical area of the logical volume to store data to the logical area, and stores the data in the allocated storage area, adds at least one of the one or more pool volumes in the second pool to the first pool, according to the status of the first pool, and adds at least one pool volume provided by storage areas of at least one storage device to the second pool, according to the status of the second pool.