To provide a storage apparatus and its control method capable of preventing degradation of sequential performance by making the page size of pages allocated to a duplicate of a logical volume an appropriate size.A storage apparatus including a controller connected to a host system and a storage device connected to the controller, wherein the controller provides the host system with a logical volume, a duplicated volume which is a duplicate of the logical volume, and a snapshot volume for storing data to be saved by a snapshot; and a page(s) is allocated in a stripe unit of data size that can be read in response to one read command to the storage device when allocating the page(s) to the duplicated volume.