Patent ID: 7747576

Claim:
A method for asynchronously transmitting one or more incremental database updates from a primary site to a remote site, the primary site and the remote site interconnected by at least one communication link, the method comprising: (a) destaging from cache memory modified data to a first volume at the primary site for a current database update and updating one or more bits in a first bitmap at the primary site that indicate one or more tracks on the first volume that are to be overwritten with the modified data, said updating one or more bits being a first point in time virtual copy of the modified data of the first volume to a second volume, wherein the first point in time virtual copy updates the first bitmap and no physical data is copied from the first volume to the second volume; (b) transferring the first bitmap to a second bitmap at the primary site for indicating the modified data that is to be transmitted to a third volume, which is at the remote site, for the current database update, the transferring including at least inverting bits of the first bitmap to the second bitmap; (c) synchronizing the second volume with the third volume for the current database update by transmitting the modified data from either the first volume or the second volume depending on bit setting in the first bitmap, to the third volume as indicated by the one or more bits in the second bitmap; and (d) performing a second point in time virtual copy of the modified data of the third volume to a fourth volume, which is at the remote site.