3DC multi-target configuration with three UR sites using delta resync
You should create a UR pair that connects the two secondary sites so that the remote copy system created with the host operation site and backup site can be created immediately in the event of a failure or disaster at the primary site. A UR pair that is created to make a triangle-shaped remote copy connection among the three sites is called a UR delta resync pair. By creating a UR delta resync pair in advance, you can transfer the copying operations from between the secondary sites back to from the primary to the secondary site in a short time when the failure is corrected and the primary site is brought back online.
The following illustration shows the 3DC multi-target configuration with three UR sites using delta resync:
