How operating system clusters work
The method of clustering that Domino uses is called "application clustering." Domino, which is an application, monitors the cluster and determines when failover and workload balancing should occur, based on parameters that you set.

Another form of clustering is "operating system clustering." In this form of clustering, the operating system monitors the cluster and determines when failover should occur. When failover occurs, the server (called a node) to which you fail over takes over the resources of the failed node, accesses the storage space the failed node was accessing, and runs the applications the failed node was running.

There are two basic methods of running operating system clusters, active-passive and active-active. In an active-passive cluster, passive nodes do not run their own applications but instead stand by to take over if active nodes fail. In an active-active cluster, the nodes all run their own applications but are also available to take over if other nodes in the cluster fail. In addition, you can configure an operating system cluster to fail over only when there is a hardware failure or to fail over when there is either a hardware failure or a software failure.

Because Domino uses application clustering, this section does not give detailed information about the various methods and configurations that operating system clusters use. However, because you can run Domino in conjunction with several operating system clusters, including IBM High Availability Cluster Multi-Processing (HACMP), Microsoft® Cluster Server (MSCS), and Sun(TM) Cluster, this section describes basic information about operating system clusters.

Note For information about configuring your operating system cluster software to run with Domino, see the documentation that came with your operating system cluster.

Operating system clusters provide failover that is transparent to users. Because the receiving node takes over the resources of the failed node, the user sees the same server name and same network address as on the original server. Unlike many operating system clusters, Domino clustering does intelligent failover. When a server fails, Domino checks its cluster cache to find the server that is most available in the cluster. Domino also lets you actively control workload balancing, which operating clusters may not offer. In addition, Domino clustering lets you set up clusters of servers that run different operating systems, while operating system clusters require that all nodes run the same operating system.

The following example shows a basic configuration for active-passive operating system clustering. A Domino server runs on Node 1. Node 2 monitors Node 1 and waits for a failure to occur.

Basic active-passive operating system cluster

When a failure occurs, Node 2 picks up the resources of Node 1 and takes over running the Domino server. Node 2 uses the same disk set and the same IP address for the Domino server that Node 1 used.

Failover in active-passive operating system cluster

To run Domino in an active-active cluster, you must use Domino partitioned servers on the nodes. Doing so lets each node take over the tasks of the other node while also maintaining its own tasks.

The following example shows a basic configuration for active-active operating system clustering. Node 1 and Node 2 each have Domino running in the first partition. The second partition on each node duplicates the resources of the first partition on the other node. Each node has its own disk set, but both nodes have access to both disk sets in case failover occurs. The nodes monitor each other.

Basic active-active operating system cluster

When Node 1 fails, Node 2 picks up the resources of Node 1 and runs the Domino servers for both nodes.

Failover in active-active operating system cluster

To use an active-active configuration, you must be sure that each node can handle the load of the other node if failover occurs.

Benefits of using OS clusters with Domino clusters

When you use an operating system cluster in conjunction with a Domino cluster, the few things that do not fail over in a Domino cluster will fail over in the operating system cluster. Here are a few examples:

For these features, it is a good idea to set up an active-passive operating system cluster to run in conjunction with the Domino cluster.

See Also