Storage system, copy method, and primary storage apparatus

A copy method for a storage system for providing a primary logical volume formed with a storage area in plural hard disks, that includes a primary storage apparatus for storing data from a host computer in the primary logical volume, and a secondary storage apparatus connected to the primary storage apparatus, for providing a secondary logical volume for storing a copy of the data, the method comprising:

• a search step for checking whether or not data exists in each primary slot area formed by partitioning a storage area in the primary logical volume into predetermined storage areas;
• a transmission step for sending, if no data is held in the primary slot area, a notice indicating no data stored to the secondary storage apparatus;
• and
• a data write step for writing, when the notice is received from the primary storage apparatus, zero data in the secondary slot area.