Storage subsystem and storage system

A storage control method implemented in a storage system, said storage system comprising a first storage subsystem and a second storage subsystem, said first storage subsystem comprising a first memory device, and said second storage subsystem comprising a second memory device, wherein, said first storage subsystem is communicably connected to a host device for sending write target data, and is communicably connected to said second storage subsystem, said storage control method comprising:

• beyond a certain timing, writing write target data sent from said host device into said first memory device;
• beyond said certain timing and when the write target data is written in said first memory device, writing pre-updated data of said write target data in a pre-updated memory region,
• wherein said pre-updated data memory region stores data that constitutes data prior to update by the write target data and constitutes data that has been written in said first memory device;
• wherein said pre-updated data memory region is a third memory device that can be configured as a pair with said first memory device, and
• providing in a physical memory device a first type logical volume, for which no specific attributes are set;
• and
• providing in a physical memory device a plurality of second type logical volumes, for which specific attributes are set,
• wherein said first memory device and said second memory device constitute said first type logical volume,
• wherein said third memory device constitutes a virtual logical volume configured from at least one of the second type logical volumes, and
• wherein a local copy means, by writing said write target data in a second type logical volume of said plurality of second type logical volumes that has a free space, writes said write target data in said virtual logical volume.