The Sun Java System Directory Server topology includes four masters and four read-only replicas. Directory Server is the corporate directory server used to control access to Web-based applications. The directory server has a single root suffix, dc=gt,dc=com; information about the users are stored in the ou=people, dc=gt,dc=example,dc=com container with uid as the naming attribute.
Two masters and two read-only replicas are located in the United States (a separate configuration directory in the United States stores configuration information for these systems).
Two masters and two read-only replicas are located in Europe (a separate configuration directory in Europe stores configuration information for these systems).
Identity Synchronization for Windows treats hub replicas the same as read-only replicas. In many scenarios, using a hub replica is preferred to using a read-only replica because a hub can be easily promoted to a master.