Patent ID: 8429339

Claim:
A storage device comprising: a first storage unit configured to store data supplied from a host; a second storage unit configured to store information for managing the first storage unit; and a control unit configured to transfer data between the host and the first storage unit, wherein the first storage unit provides blocks, each of the blocks including pages; the second storage unit has a free block list holding information about which blocks of the blocks provided in the first storage unit can be written, and a free page list holding information about which pages of the pages provided in the first storage unit can be written; and when the control unit transfers the data supplied from the host to the first storage unit, the control unit generates compressed data blocks by compressing the data supplied from the host in units of blocks, writes the compressed data blocks to the blocks which can be written in accordance with the information held in the free block list, holds, in the free page list, information about pages existing in free areas, which are pages in the blocks holding compressed data blocks and which do not hold compressed data blocks, and writes additional data supplied from the host in units of pages to the pages existing in the free areas, in accordance with the information held in the free page list.