Synchronization and resynchronization of loosely-coupled copy operations between a primary and a remote secondary DASD volume under concurrent updating

A method for assuring consistency between a primary volume and a remote secondary volume wherein a host CPU manages track-to-track transfers using loosely-coupled, storage control unit mediated, data paths. The method includes initial volume synchronization in which concurrent updates to primary tracks are serialized by the copy progression at the secondary volume according to address. The method further includes volume resynchronization in the event of extrinsic error, fault, or the like in which the status of primary tracks updated during a volume suspension interval utilize bit maps to determine status of tracks unmodified during the suspension interval, and updated tracks and timestamps in addition to addresses. The bit maps and timestamps preserve the most recent version copy order of the tracks on the secondary volume.