Clustering

Windows 2000 Advanced Server supports two different kinds of clustering, either of which can greatly improve your fault tolerance:

• For many TCP/IP-based applications, the Network Load Balancing service provides a simple, "shared nothing," fault-tolerant application server.
• Server clusters provide a highly available fault-tolerant environment that can run applications, provide network services, and distribute loads.

Network Load Balancing

The Network Load Balancing service (called Windows Load Balancing Service in Microsoft Windows NT 4) allows TCP/IP-based applications to be spread dynamically across up to 32 servers. If a particular server fails, the load and connections to that server are dynamically balanced to the remaining servers, providing a highly fault-tolerant environment without the need for specialized, shared hardware. Individual servers within the cluster can have different hardware and capabilities, and the overall job of load balancing and failover happens automatically, with each server in the cluster running its own copy of Wlbs.exe, the Network Load Balancing service.

Server Clusters

Server clusters, unlike network load balancing, depend on a shared resource between nodes of the cluster. This resource, which in Windows 2000 Advanced Server, as shipped, must be a shared disk resource, is generally a shared SCSI or Fibre Channel-attached disk array. Each server in the cluster is connected to the shared resource, and the common database that manages the clustering is stored on this shared disk resource.

Nodes in the cluster generally have identical hardware and identical capabilities, although it is technically possible to create a server cluster with dissimilar nodes. Microsoft Windows 2000 Advanced Server supports up to two node server clusters, whereas up to four nodes are supported in Datacenter Server.

Server clusters provide a highly fault-tolerant and configurable environment for mission-critical services and applications. Applications don't need to be specially written to be able to take advantage of the fault tolerance of a server cluster, although if the application is written to be clustering aware, it can take advantage of additional controls and features in a failover and fallback scenario.