There is provided a computer system which can implement ease of transition to a standby state caused by power-off of a volume and ease of recovery from a standby state while maintaining access performance. A computer system including a storage system (200) having one or more disk units (220) and a disk controller unit (210) which controls reading and writing of data stored on volumes formed by the disk units and a host computer (100) which transmits a data read/write request to the storage system (200), wherein the host computer (100) gives an instruction to perform volume assignment for each of groups each having duplicated sets obtained by multiply duplicating a set composed of one or more volumes on which data is to be stored, and the storage system (200) assigns a first volume of a first duplicated set in the group to one of the disk units (220) which has an attribute different from an attribute of a volume constituting another duplicated set.