The global administrator in OUD is responsible for managing and maintaining administrative server domains in replicated environments. When you configure replication for the first time, OUD 11g creates a directory entry for the global administrator in the cn=Administrators, cn=admin data subtree.
While the global administrator user is typically created when you configure replication, this user is not limited to administering replication. You can perform any administrative task when you log in to OUD as the global administrator user. The cn=admin data naming context is automatically replicated throughout a replication topology to ensure that the global administrator user is available on all replicas in the topology.
Login into Topology Manager in ODSM using admin user.
Details of Replication Server and replicated data can be seen here.