Patent ID: 7734883

Claim:
A method for forming a consistency group of data, comprising: providing information on a consistency group relationship indicating a plurality of slave controllers and, for each indicated slave controller, an indicated portion of a slave storage unit managed by the slave controller, wherein the slave controllers indicated in the consistency group transmit data from the indicated portions of their respective slave storage units consistent as of a point-in-time; transmitting a command to each slave controller in the consistency group relationship to cause each slave controller to transmit data in the portion of the slave storage unit to a remote storage in a manner that forms the consistency group; determining whether all the slave controllers successfully transmitted the data in the portions of the slave storage units that is part of the consistency group to the remote storage; and copying data from a plurality of local controllers at a local site to the slave controllers at an intermediate site to store in the slave storage units, wherein the local controllers and slave controllers are at different geographical sites and the remote storage is at a remote geographical location with respect to the geographical sites including the local and slave controllers.