An apparatus, system and method for synchronizing an asynchronous mirror
volume using a synchronous mirror volume by tracking change information
when data is written to a primary volume and not yet written to an
asynchronous mirror, and storing the change information on both the
primary storage system and the synchronous mirror system. In the event
the primary storage system becomes unavailable, the asynchronous mirror
is synchronized by copying data identified by the change information
stored in the synchronous mirror system and using the synchronous mirror
as the copy data source.