a data mirroring method makes it possible to change the data mirroring mode among three kinds of data mirroring modes with the three kinds of modes according to the degree of burdens on the hosts and the respective controllers . a first information processing apparatus has a first host and a first disk system for sending and receiving data to and from the first host . a second information processing apparatus has a second host and a second disk system which connects the first disk system and the second disk system to each other and makes the data common to the first disk system and the second disk system . the disk mirroring method selects one of the three data mirroring modes including a synchronous mode , a semi - synchronous mode and an adaptive copy mode being different in data processing speed form one another according to the quantity of operations of the first host .