## Server Clusters

A cluster is group of servers linked together to perform a common task.

Clusters provide the following features:

• High availability—If one server in the cluster goes down, the work assigned to that server is migrated to another server in the cluster.

• Load balancing—Clusters allow work to be distributed across different servers.

Clusters can use the shared model or the nonshared model. The shared model requires distributed lock manager (DLM) to manage concurrent access to shared resources. The nonshared model does not require DLM and as a result, requires less overhead. For example, the MSCS (Microsoft clusters) use the nonshared model. This means that a node owns a resource and another node takes ownership of that resource when the owner node fails.

For more information on Cluster-Quorum, see the “Cluster Quorum”.