A storage device is provided, which allows a write area associated with a data area of interest to be allocated according to write performance of a host computer. The storage apparatus includes one or more flash memory packages having a plurality of flash memories and stores data transmitted from one or more host computers. A storage area provided by the one or more flash memory packages includes a first area that is an area for storing actual data formed by one or more logical devices and a second area that is an area for storing a write instruction from the host computer to the logical device. The first and second areas are provided in each of the one or more flash memory packages. The apparatus further includes a monitoring section monitoring the frequency of write instructions from the host computer and a changing section for changing the size of the second area according to the frequency of write instructions.