Server clustering is one of the most useful options of Domino. In a cluster, a set of Domino servers mirror one another's operations. Clustering is similar to standard database replication, except that it is very fast. Changes made to one server are copied to the other cluster members within a few seconds. Clustering offers a large number of benefits for a small price. Here are a few:
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- Redundancy for critical servers and databases. If a cluster member fails, users are automatically directed to a running cluster member, which will have up-to-date data.
- Increased load handling, because multiple servers are available to users instead of one machine.
- Automatic load balancing among cluster members, so users are directed to the server with the lightest load.
Here are a few things to keep in mind if you create a cluster for your Domino server or are thinking about doing so:
- Make sure you have the Enterprise or Utility licenses for the Domino servers, as these are the licenses that support clustering.
- By default, all databases with the same replica IDs that exist on both servers will mirror each other's activity in real time across the cluster. In practice, it is important to manually check which databases are configured to operate in this way. Using the Domino Administrator program, open the Cluster Database Directory (CLDBDIR.nsf) on each clustered server. Select the view Databases By Pathname, review the list of databases there and see whether cluster replication is enabled or disabled for each.
- Physically separate the cluster members as much as possible to reduce the chance of a common accident befalling them. If there is a fire in the server room, you don't want both members of a cluster in that one room. Ideally, cluster members should be in separate buildings, on separate power supplies, connected by a high-speed LAN. If separate buildings are not available, the cluster members can be located in different parts of the same building on different circuit breakers.
- Domino clustering contains an option to create a separate LAN specifically for cluster replication traffic. This LAN is used only for server-to-server communication, freeing the regular LAN for user traffic. If server performance is the prime consideration, I recommend setting up this special LAN.
Chuck Connell is president of CHC-3 Consulting, which helps organizations with all aspects of Domino and Notes.