Sizing Network Load Balancing clusters

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Sizing Network Load Balancing clusters

Cluster size, defined as the number of cluster hosts participating in the cluster (up to 32), is based on the number of computers required to meet the anticipated client load for a given application.

If, for example, you determine that you need six computers running Microsoft Internet Information Services to meet the anticipated client demand for Web services, then Network Load Balancing will run on all six computers, and your cluster will consist of six cluster hosts.

As a general rule, add servers until the servers can comfortably meet their demands without saturating the network. The exact number depends on the nature of the application. When the cluster subnet approaches saturation, add clusters using round-robin DNS. The maximum cluster size is determined by network capacity. The minimum cluster size is determined by server capacity. For example, if two extremely powerful servers can take the place of six less powerful servers, your entire cluster will consist of only two cluster hosts. In addition, you should always make sure that there is enough extra server capacity so that if one server fails, the server next in line will not fail, which would create a cascading series of server failures.

Notes

  • If you deploy two or more clusters, consider putting them on individual switches so that incoming cluster traffic is handled separately. For more information on using Network Load Balancing hosts on switches, see article Q238219, "How Network Load Balancing Hosts Converge When Connected to a Layer 2 Switch," and article Q193602, "Configuration Options for WLBS Hosts Connected to a Layer 2 Switch," in the Microsoft Knowledge Base.

  • Before load balancing an application in a Network Load Balancing cluster, review the application license, or check with the application vendor. Each application vendor sets its own licensing policies for applications running on clusters.