Difference between load balancing and clustering

The NLB service provides a means for load balancing TCP/IP traffic among multiple servers in an NLB cluster. The servers participating in the NLB cluster do not share storage or other resources, but instead run their own instances of the load-balanced applications. For i, each server would run IIS with an instance of the same Web site, but each would be a separate copy. NLB simply manages the incoming traffic and balances it out to the servers participating in the cluster.

NLB provides no failover capability, but the Cluster Service does provide redundancy and failover capability. Servers in this type of cluster generally share common storage and function as a single, logical unit. By contrast, an NLB cluster is a group of individual servers working independently to process the traffic that the NLB service passes their way. Essentially, the NLB service enables all servers in the NLB cluster to be addressed by a single IP address. You can combine NLB clustering with Cluster Service clusters, but these two cluster types must remain separate; that is, a server can't participate in both types of clusters. The usual solution is to build an NLB cluster upstream to service a Cluster Service cluster

What's New in Clustering Technologies
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