The storage system provides a logical volume and includes a plurality of disk devices and a controller, coupled to the plurality of disk devices, which manages a plurality of storage areas provided by the plurality of disk devices. The host includes an application which sends data to a logical volume and an operating system which manages a block position of the logical volume. If the operating system receives a request from the application to expand a first capacity of the logical volume, the operating system sends a write request to the logical volume. In response to the write request, the controller allocates at least one of the plurality of storage areas to the logical volume. The controller monitors a second capacity of storage areas allocated to the logical volume relative to a third capacity of the plurality of storage areas.