This storage system comprises a block interface, a block control unit, a file control unit, and shared memory. The file control unit and block control unit are coupled via a first memory-through path structured to pass through a first area of the shared memory, and via a second memory-through path structured to pass through a second area of the shared memory. The block control unit has a protocol control unit and a virtual driver; exchanges control information for the file control unit with the file control unit via the first memory-through path; uses the virtual driver to convert an I/O request passed from the file control unit via the second memory-through path and processes the result with a protocol processing unit; and bypasses the virtual driver and uses the protocol processing unit to process a block I/O request transferred from the block interface via a physical path.