Patent ID: 7908446

Claim:
A copy system for copying data written from a host into a first volume on a primary system to a second volume on a secondary system synchronously or asynchronously with writing of said data, comprising: a first control unit provided to said primary system for using a first bitmap to reflect changes to an area in said first volume to which data was written from said host, creating a second bitmap reflecting contents of said first bitmap during initial copy that matches contents of said first and second volumes prior to said copy, sending said second bitmap to said secondary system, and copying to said second volume only valid data containing data written by said host in said first volume based on said second bitmap; and a second control unit provided to said secondary-system for creating a third bitmap, contents of which is merged with contents of said second bitmap sent from said primary-system, and reflecting a differential indicating differences in content between said first and second volumes during said initial copy based on said third bitmap.