Storage device utilizing free pages in compressed blocks

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.