Types of Replica

A database that participates in replication is called a replica. There are three kinds of replica:

• A master replica is a read-write database that contains a master copy of the directory data. A master replica can perform the following tasks:

  • Respond to update requests and read requests from directory clients

  • Maintain historical information and a change log for the replica

  • Initiate replication to consumers or hubs

• A consumer replica is a read-only database that contains a copy of the information held in a master replica. A consumer replica can perform the following tasks:

  • Respond to read requests

  • Maintain historical information for the replica

  • Refer update requests to servers that contain a master replica

• A hub replica is a read-only database, like a consumer replica, but stored on a directory server that supplies one or more consumer replicas. A hub replica can perform the following tasks:

  • Respond to read requests

  • Maintain historical information and a change log for the replica

  • Initiate replication to consumers

  • Refer update requests to servers that contain a master replica

A single instance of Directory Server can be configured to manage several replicas.

A replica can act as a supplier of updates, or a consumer of updates, or both.

• A supplier is a replica that copies information to another replica.

  A master replica can be a supplier to a hub replica and a consumer replica. A hub replica can be a supplier to a consumer replica. In multi-master replication, one master replica can be a supplier to another master replica.

• A consumer is a replica to which another replica copies information.

  A hub replica and a consumer replica can be consumers of a master replica. A consumer replica can be a consumer of a hub replica. In multi-master replication, one master replica can be a consumer of another master replica.

A replica can be promoted or demoted to change its behavior with respect to other replicas. Dedicated consumers can be promoted to hubs, and hubs can be promoted to masters. Masters can be demoted to hubs, and hubs can be demoted to dedicated consumers.

A server that contains a consumer replica only is called a dedicated consumer.