Build an Exchange 2003 Cluster—Part 1: Plan and Prepare

Clustering Microsoft Exchange Server 2003 servers can potentially improve service levels by reducing downtime—especially planned downtime, when you have to reboot servers after applying monthly Microsoft patches. Windows Server 2003 includes enhancements that make setting up and deploying a cluster much easier than under Windows 2000 Server. If you believe clustering can benefit your Exchange organization and are ready to get started, this article can help guide you through the cluster-setup process. In part 1, I explain Exchange clustering basics and the preparatory steps you must take before building a new two-node Exchange 2003 Service Pack 1 (SP1) cluster running on Windows 2003 SP1. Part 2, which will appear in an upcoming issue of Windows IT Pro, will explain how to install Exchange 2003 on a Windows 2003 SP1 cluster and post-installation best practices.

Exchange Virtual Servers
Clusters are groups of servers configured to work together to provide the image of a single server. Microsoft Outlook clients access Exchange running on a cluster via the Exchange Virtual Server (EVS) service. To a user, an EVS looks like a typical standalone server. An EVS contains these Exchange cluster resources:

Before you can install an EVS, you must manually create the following cluster resources by using the Cluster Administrator program:

Later I'll outline the steps for creating an Exchange cluster group and the resources that the EVS requires. When you configure an Exchange 2003 cluster, the Exchange Setup program places all these resources in a resource group (called an Exchange cluster group). An EVS can't be split across separate resource groups, which ensures that the resources and virtual servers all fail over as a single unit and that resource-group integrity is maintained.

Exchange Cluster Models
Exchange 2003 supports two cluster models: active/active (two-node clusters only) and active/passive (two- to eight-node clusters). A node is considered active if it hosts an EVS and passive if it doesn't host an EVS. Active/active clusters were first introduced in Exchange 2000 Server, and for backward-compatibility reasons, Microsoft continues to support them in Exchange 2003. Because of scalability limitations of active/active clusters, Microsoft's recommended cluster model for Exchange 2003 and Exchange 2000 is active/passive.

Although active/active clusters appear to be an attractive proposition (no servers are sitting idle waiting for a failover to occur), they have limitations. Early deployments of active/active clustering on Exchange 2000 had virtual memory problems, which led Microsoft to state that the maximum number of concurrent Outlook client connections that a node could support under Exchange 2000 release to manufacturing (RTM) was 1000. Microsoft made some improvements to Exchange 2000 SP1 and SP2 that allowed an active/active cluster to support more connections (1500 for SP1; 1900 for SP2). The 1900 limit in Exchange 2000 SP2 still applies to clusters running Exchange 2000 SP3, Exchange 2003 RTM, or Exchange 2003 SP1. Virtual memory fragmentation is less of an issue on active/passive clusters because an EVS can always be started on a passive cluster node (there's no active EVS on the passive node, so virtual memory fragmentation isn't an issue).

Additionally, active/passive clusters don't have the same constraints on the numbers of supported connections as active/active clusters. As I mentioned, Exchange 2003 SP1 supports a maximum of 1900 concurrent connections per node in an active/active configuration. A connection in this context means an active Outlook, Microsoft Outlook Web Access (OWA), or Outlook Express client connection and shouldn't be confused with the number of mailboxes residing on an Exchange server. Because of scalability limitations of active/active clusters, Microsoft's recommended cluster model for Exchange 2003 and Exchange 2000 is active/passive. With an active/passive cluster, the 1900-connections limit doesn't apply. In Exchange 2003, Microsoft has built functionality into Exchange System Manager (ESM) that enforces active/passive clustering guidelines on clusters that have more than two nodes. (You can find more information about these guidelines at http://support.microsoft.com/?kbid=329208.) You can create n − 1 EVSs, where n represents the number of nodes in the cluster. ESM prevents you from creating EVSs that equal or exceed the number of nodes in the cluster.

Preparing Your Cluster for the Exchange Installation
Planning is an essential ingredient in a successful Exchange 2003 cluster deployment. It involves considerations such as training, choosing a cluster model, choosing hardware and storage, and setting permissions. In the Web-exclusive sidebar "Planning Your Exchange Cluster Deployment," http://www/windowsitpro.com, InstantDoc ID 46687, I discuss Exchange cluster-planning considerations in detail.

After you've planned the Exchange cluster and created the Windows 2003 cluster, you're almost ready to begin installing Exchange 2003 on it. But before you install Exchange, you need to perform some additional tasks and checks to avoid problems during the installation.

Install layered products that Exchange requires. Exchange requires several Windows components, which you install via the Add or Remove Programs applet. You need to install these components on both cluster nodes. To install the components, in Add or Remove Programs click Add/Remove Windows components, check Application Server, click Details, and check ASP.NET and Internet Information Services (IIS). Click Details, then check Common Files, NNTP Service, SMTP Service, and World Web Service. Click OK to close each box and install the components.

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