A replication system capable of automatically forming an authentic copy pair with a primary volume at a copy destination system without depending on an operator and realizing the pair formation without labeling a tape is provided.A system for performing initial copying of data of a copy source volume from a portable storage medium storing the data of the copy source volume to a copy destination volume is characterized in that the portable storage medium stores management information about the copy source volume, wherein a system to which the copy destination volume belongs copies data of the portable storage medium to copy destination volume information, reads the management information from the copy destination volume, and sends it to a system to which the copy source volume belong; and this system judges whether these pieces of information are authentic or not; and if an affirmative judgment is returned, it is determined that the copy source volume and the copy destination volume constitute an authentic copy pair.