A control unit of a hierarchical control apparatus holds information in which one of duplexed library apparatuses is set as a master and the other is set as a slave for each medium in each of the duplexed library apparatuses, and statistical information about each of the library apparatuses. The control unit includes an automatic redundant copy unit detecting that a statistical information of a medium reaches a predetermined amount, replacing the medium with a free medium, and copying data to the free medium, a master/slave setting unit setting the medium to which the data is copied and the other medium as a master or a slave such that a load is even between the duplexed library apparatuses according to the statistical information, and a unit copying and reading the requested data to the disk array apparatus by prioritizing one of the duplexed library apparatuses including the medium set as a master when there is no requested data in the disk array apparatus.