Replication enables geographic distribution of the directory service by providing identical copies of directory data on multiple servers across more than one data center. The basic principles of a replication deployment outlined in the small topology also apply to multiple data center deployments.
The Sun OpenDS Standard Edition directory server uses a custom replication protocol that is efficient over a wide area network (WAN). In the following scenario, an enterprise has two major data centers, one in London and the other in New York, separated by a WAN.
This deployment includes two replication server instances for availability in each data center, in case one of the replication server instances fails. The directory servers connect first to local replication servers. Directory servers only access replication servers in another data center if all local replication servers have failed. Client applications always connect to local directory server instances, and perform reads and writes on the same directory server instance.
The Sun OpenDS Standard Edition directory server supports an unlimited number of read/write directory servers in a replication topology. The number of directory servers can be scaled according to the read requirements of the organization. Note that increasing the number of directory servers does not scale the number of writes that can be processed because ultimately all servers in the toplogy must process all the writes. Unless it is acceptable to have a topology that does not converge, the write throughput of the topology is limited to the write throughput of the slowest machine.