Server apparatuses that configure a data mirror cluster system include databases, shared memories, and memory controllers, respectively. The server apparatuses are connected by interconnects and can directly access communication partner's shared memories via the memory controllers, respectively. One of the server apparatuses operates as an operation server apparatus and the other operates as a standby server apparatus. The memory controller of the operation system updates the database and writes changed data to the shared memory of the standby system. The memory controller of the standby system updates the database of the standby system according to the changed data written to the shared memory of the standby system.