NLB for Scalability

Applies To: Windows Server 2003 with SP1

Q. How Large Should My Cluster Be?

A. The size of the cluster is determined by the application that is being hosted and load balanced and on the system resources on the host machines available to service client requests sent to the application. If you notice that client requests are slowing down as more and more clients make connection requests to the application, it may be time to add more hosts to the cluster. A single NLB cluster can have up to 32 hosts in it.

For more information and examples of how to determine the size of your cluster refer to Chapter 10 Designing Network Load Balancing of the Windows Server 2003 Deployment Guide, (

Q. Are There Any Performance Concerns as My Cluster Grows?

A. Tests have shown the NLB performance begins to deviate from the linear as the cluster grows beyond 20 to 25 nodes. But, this really depends on the amount of traffic that the application sees in the form of client requests. The following graphs give a better idea of NLB performance as the cluster size and number of users increase.

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Q. We Expect Our Front-End Cluster to Grow Beyond 32 Nodes. Should I Use NLB Even Though it Has a Cluster Size Limit of 32 nodes?

A. NLB can be used to scale beyond 32 machines by using Round Robin DNS between multiple NLB Clusters. This is shown in the following figure.

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