Active Directory Replication

Replication Model Components

The following mechanisms contribute to the overall replication system:

Multimaster loose consistency with convergence, which maintains data integrity.
- "Multimaster" means that a directory partition can have many writable replicas, or copies, that must be kept consistent between domain controllers in the same forest. The replication system propagates changes made on any specific domain controller to all other domain controllers in the forest that store the directory partition in which the change occurs.
- "Loose consistency" means that the replicas are not guaranteed to be consistent with each other at any particular point in time because changes can be applied to any full replica at any time.
- "Convergence" means that if the system is allowed to reach a steady state in which no new updates are occurring and all previous updates have been completely replicated, all replicas are guaranteed to converge on the same set of values.
Store-and-forward replication, which means that changes are not sent directly from one domain controller to all other domain controllers. Instead, a change is sent directly to only a subset of domain controllers. This subset of domain controllers is then responsible for sending the change to other domain controllers, and so on, until the change has reached every domain controller.
Pull replication, which means that domain controllers request (pull) updates from replication partners. The domain controller in which a change originates does not "push" the change unsolicited to other domain controllers.
State-based replication, which means that instead of storing a full change log, each directory partition replica stores per-object and per-attribute data to support replication.