Asynchrones Datenfernkopieren

Asynchronous remote data duplexing at a distant location is performed from copies based at a primary site storage subsystem using first and second pluralities of subsystems 12, 14 at primary and remote sites respectively. Each of the first plurality of subsystems is independently coupled to one or more of the second plurality of subsystems. The first plurality of subsystems are interconnected and the second plurality of subsystems are also interconnected. The method utilizes checkpoint messages to maintain sequence integrity between the first and second plurality of subsystems without the use of a centralized communications service.