US Patent 7100089 Determining differences between snapshots

A method is provided for synchronization of a backup copy of a volume of memory represented by a snapshot tree. The snapshot tree includes a plurality of snapshot volumes, each snapshot volume corresponding to a respective snapshot of the volume of memory. The method comprises the following: determining whether there are any exceptions in any of the snapshot volumes in the snapshot tree between and including the snapshot volumes corresponding to a first and a second snapshot; if there are exceptions, processing for the exceptions to synchronize the backup copy of the memory volume; otherwise, if there are no exceptions, ignoring the snapshot volumes.