Clustering is a feature in Windows 2000 Server that you can use to achieve scalability and high availability for server applications such as Exchange 2000.

A cluster consists of individual computers (also called nodes) that function cohesively in a cluster service. These computers act as network service providers or as reserve computers that take over server operations for another node if it experiences problems. Clustering provides increased scalability, fault tolerance, and reliability. Furthermore, depending on how your cluster is configured, clustering can simplify the process of recovering a single server from disasters.

In a clustering environment, Exchange 2000 runs as a virtual server (not as a stand-alone server) because any node in a cluster can assume control of a virtual server. If the node running the Exchange virtual server experiences problems, the Exchange virtual server goes offline for a brief period until another node takes control of the damaged node.

You can use either an active/passive or active/active configuration for your Exchange 2000 clusters.

• Active/Passive Clustering In active/passive clustering, the cluster includes a primary node and one or more secondary nodes. The secondary nodes are idle until a failure occurs on a primary node. When the primary node in an active/passive cluster fails or is taken offline, the clustering feature in Windows 2000 takes over. The failed node is taken offline, and a secondary node takes over the operations of the failed node. It usually only takes a few minutes for the cluster to fail over to another node. As a result, the Exchange 2000 resources on your cluster are unavailable to clients for only a brief period of time.
• Active/Active Clustering In active/active clustering, all nodes in your cluster group are active (that is, they each share the processing operations of the Exchange 2000 cluster). When one node in an active/active cluster fails or is taken offline, the remaining nodes in the cluster take over for the failed node.

The clustering process allows you to manage a group of independent servers as a single system. Each server in the cluster has individual memory, processors, and network adapters, but shares a common storage medium.
Each server also has an identical processor and the same amount of RAM. A separate private network, used only for cluster communication between the nodes, can connect these servers.

Note Although it is possible to configure Exchange 2000 to support multiple virtual servers on a single node, it is recommended that only one virtual server run on each node in the cluster.

When you configure an Exchange 2000 cluster, you must create groups to manage both the cluster and the Exchange virtual servers in the cluster. Furthermore, you can independently configure each Exchange virtual server. When creating cluster groups, consider the following recommendations:

• When creating groups within Cluster Administrator, create a separate group for the quorum disk resource to provide fault tolerance for the cluster.
• Each group should have its own set of physical hard disks assigned to the cluster resources in that group. As a result, if an individual hard disk fails, cluster resources in other groups are not affected.
• Use separate physical hard disks to store an Exchange virtual server's transaction log files and database files. This prevents a single hard disk failure from eliminating both the log files and database files for that Exchange virtual server. This recommendation is also relevant for Exchange 2000 stand-alone servers.

The information in this article applies to:

• Microsoft Exchange Server 2003 Enterprise Edition
• Microsoft Exchange Server 2003 Standard Edition
• Microsoft Windows Small Business Server 2003, Premium Edition
• Microsoft Windows Small Business Server 2003, Standard Edition
• Microsoft Exchange 2000 Server