Asynchronous remote data copying using subsystem to subsystem communication

A method and means for asynchronous remote data duplexing at a distant location from copies based at a primary site storage subsystem in which there are first and second pluralities of subsystems 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. Further, the first plurality of subsystems is interconnected, and the second plurality of subsystems is 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.