Patent ID: 7966463

Claim:
A control method for an asynchronous remote copy system in which, from among a plurality of storage control apparatuses, a primary volume and a secondary volume are set and data is transferred asynchronously from the primary volume to the secondary volume, the method comprising: a first step of setting a primary volume in a first storage control apparatus; a second step of setting a secondary volume in a second storage control apparatus; a third step of interrupting a current cycle in progress of the asynchronous remote copy from the primary volume to the secondary volume; a fourth step of storing data in the secondary volume; a fifth step of determining a certain area in the secondary volume, the certain area containing data required to be copied from the secondary volume in which the data has been stored to the primary volume, the certain area including: an area to which primary volume difference data is written during the current asynchronous remote copy cycle; an area to which data is written by a second host system after the operation of a first host system is taken over by the second host system; and an area that corresponds to an area in the primary volume to which data is written by the first host system after the current asynchronous remote copy cycle is started and until the operation of the first host system is taken over by the second host system; a sixth step of shifting the primary volume in the first storage control apparatus to serve as a secondary volume; a seventh step of shifting the secondary volume in the second storage control apparatus to serve as a primary volume; an eighth step of copying the data in the certain area to the primary volume; and a ninth step of restarting the asynchronous remote copy from the primary volume in the second storage control apparatus to the secondary volume in the first storage control apparatus.