Creating substitute area capacity in a storage apparatus using flash memory

A storage area creation method for a storage apparatus, the method being implemented in a first storage apparatus included in a computer system, the computer system comprising the first storage apparatus, which includes one or more flash memory modules and a cache memory, a second storage apparatus, which is connected to the first storage apparatus and includes one or more hard disk drives, and a host computer connected to the first storage apparatus,

• wherein when the first storage apparatus receives a request for creation of a first storage area to be realized with a logical device formed with one or more flash memory modules, the first storage area having a relationship of a copy pair with a second storage area, the first storage apparatus creates the logical device, which is formed with one or more flash memory modules incorporated in the first storage apparatus, according to a capacity calculated by adding up the capacity of a storage area to be provided for the host computer and a substitute area capacity, and
• wherein the first storage apparatus defines the substitute area capacity according to a useful life span of the one or more flash memory modules forming the logical device and a writing access frequency for the second storage area.