US Patent 7546485 Method and system for efficient journal-based resynchronization

Various method and system embodiments of the present invention employ enhanced journal-based resynchronization for resynchronization of a primary volume to a remote secondary volume following restoration of a communications link or another event. Enhanced journal-based resynchronization involves maintaining a filled journal after the primary component system has resorted to bitmap-based journaling. Following communications-link restoration, or another event, enhanced resynchronization analyzes various values maintained by the primary component system to characterize the journaling state in order to determine whether or not to first merge the filled journal with the track-based bitmap before carrying out bit-map-based resynchronization, or to instead unspool the filled journal and transmit the unspooled WRITE requests to the second component system prior to separately carrying out bit-map-based resynchronization.