The Global Cardholder Synchronizer role ensures the two-way synchronization of shared cardholders and their related entities between the local system (sharing guest) where it resides and the central system (sharing host).
Only a single instance of this role is permitted on each system.
The guest-to-host synchronization is always performed immediately by the GCS role, because all changes to the global partitions must be validated by the host system before they can be accepted by the guest system. The host system processes the change requests on a first come, first served basis. The Global Cardholder Synchronizer (GCS) role must stay connected to the sharing host to keep the local copies of the global entities synchronized with the host.