Provided are a storage system and its control method having superb functionality of being able to notify an administrator of the extent of impact of a pool fault in an easy and prompt manner. The foregoing storage system and its control method manage a storage area provided by a storage medium by dividing it into multiple pools, provide a virtual logical device to a host system, dynamically allocate a storage area to the logical device according to a data write request from the host system for writing data into the logical device, move data that was written into the logical device to another pool according to the access status from host system to such data, identify, when a fault occurs in any one of the pools, an extent of impact of the fault based on the correspondence relationship of the logical device and the pool, and notify the identified extent of impact of the fault to an administrator.