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Master and Replica Servers

In an environment in which there are master and replica servers for an Open Directory domain, you can use these roles in a backup process. The most obvious example is that clients can failover to a replica server while you make a backup of the master server’s databases as described above. The master server’s databases are those that are most critical. Although clients can authenticate based on replica servers, and password changes can be written to replica servers and then reconciled to the master server, replicas primarily exist to act as duplicates of the master server. (This is different from Microsoft Active Directory, in which all domain controller’ share responsibility for each piece of directory data.)

You can also promote an Open Directory replica to the role of Open Directory master. This process is most often done in the event of a hardware failure, however, because if you are trying to resolve an issue of corruption of Open Directory, the corruption probably has been populated to the replica(s). If you have a very slow replication schedule (usually for situations in which there is limited bandwidth between Open Directory servers), you might be able to verify the integrity of the data on the replica and then promote the replica. You would then need to reformat the original master server and add it back into the domain as a replica, which might not be an effective strategy depending on your network configuration.

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