Abstract: The present invention pertains to a data recording control method of a magnetic tape in which tape a data, constructed by combining a plurality of packets into physical blocks, is recorded, the method being such that: the entire physical block of data is read from a magnetic tape and store in a buffer, when a command for reading a data corresponding to a packet in the physical block is output from a host unit; a new physical block is created by reorganizing the data in the buffer and the data to be recorded, when a write command and the data to be recorded are output from the host unit at any position in the physical block on the magnetic tape; and the data thus reorganized into a physical block is recorded on the magnetic tape.