Copies of data that are stored on tracks of a primary disk volume and a backup disk volume are synchronized by a method which reduces the amount of data that is transferred. The primary disk volume includes tracks with current data (i.e., non-empty tracks) and tracks with no current data (i.e., empty...http://www.google.de/patents/US6073221?utm_source=gb-gplus-sharePatent US6073221 - Synchronization of shared data stores through use of non-empty track copy procedure
