The invention proposes a directory server system having a master server and a non-master server, each server being capable of storing directory server data comprising updates. The master server is capable of sending selected updates to the non-master server, and the non-master server (512) has: a dependency checker (5224) operable for determining whether each update received from the master server (510) depends on other updates among the selected updates, and if not for sending the update to an update application function (5220), the update application function being operable for applying the updates received from the dependency checker in the non-master server directory server data.