Storage apparatus and control method of storage apparatus

A method for controlling a storage apparatus having a plurality of logical volumes, each providing a data storage area to an external device, the storage apparatus having a storage device providing a physical storage area and a storage controller managing the storage device, the method comprising:

• by the storage controller, creating a plurality of unit physical storage area from the storage device;
• by the storage controller, operating each of the logical volumes as a virtual volume in which, in response to a data IO request from the external device, the unit physical storage area is added to each of the logical volumes;
• by the storage controller, selecting any one of the logical volumes as a primary volume, selecting any one of the rest of the logical volumes as a secondary volume, the primary volume and the secondary volume being configured as a copy pair in which data in the primary volume can be copied to the secondary volume;
• and
• by the storage controller, in the case that the primary volume receives a discarding request for the unit physical storage area from the external device, determining whether or not the unit physical storage are exists, the unit physical storage area configuring the secondary volume corresponding to the unit physical storage area being a target of the discarding request, in the case that it is determined that the unit physical storage area configuring the secondary volume exists, transmitting to the secondary volume an instruction for discarding the unit physical storage area assigned to the secondary volume.