In the write processing, the storage controller 10 checks the states 523 of the extents 40 in the extent state management table 520 and determines whether any extent 40 in the open state exists or not (step S101). Specifically, the storage controller 10 checks whether any state 523 indicating “OPEN” exists or not. The storage controller 10 determines that any extent 40 in the open state exists if any state 523 indicating “OPEN” exists, or determines that any extent 40 in the open state does not exist if any state 523 indicating “OPEN” does not exist.

If any extent 40 in the open state does not exist, the storage controller 10 carries out open processing (see FIG. 13) including changing any of the extents 40 into the open state (step S102).

If any extent 40 in the open state exists in step S101 or if step S102 has been ended, the storage controller 10 determines an entry 42 to be a recording destination (addition destination) of data, based on the next entry ID 524 and the offset 525 that correspond to the extent ID of the extent 40 in the open state in the extent state management table 520 (step S103).