Implementing Fault-Tolerant Exchange Systems

Exchange administrators must design and implement Exchange messaging environments that can support the demanding uptime needs. Leveraging Windows Server 2003 clustering features, organizations can implement Exchange messaging systems with fault tolerance.

NOTE

When installing Exchange Server 2003 on a clustered Windows 2003 node, the Exchange 2003 installation automatically installs the cluster-aware Exchange 2003 version.

Preparing to Install Exchange 2003 Clusters

With a good understanding of the functionality and options of clustering with Exchange 2003 environments, administrators can begin implementing Windows 2003 in a cluster and place Exchange 2003 virtual servers in the cluster in multiple ways:

• New Installation All Exchange 2003 preparation tasks , including ForestPrep and DomainPrep, are performed prior to implementing Exchange 2003 into the clustered environment.

  NOTE

  For more information regarding preparing, planning and deploying Exchange 2003, see Chapter 2, "Planning, Prototyping, Migrating, and Deploying Exchange Server 2003."

  
  

• Post First Server Clusters can be used to add functionality to an already prepped and functional Exchange 2003 environment and Active Directory forest, allowing services' and users' mailbox information to be migrated to the Exchange 2003 and clustered virtual servers.

• Coexistence Leveraging coexistence and compatibility, Exchange 2003 clusters can be implemented in the same environment as an existing Exchange 2003 server, providing additional functionality such as Outlook Web Access (OWA) services and load-balanced mailboxes during large organizationwide growth periods.

This section introduces the features available with the cluster version of Exchange 2003 ”what it is and how it is installed. In addition, you explore the steps administrators are required to perform when implementing and configuring Windows 2003 server clusters to support the Exchange 2003 platform.

General Features Overview

Although there are no management tools installed with the Exchange installation to configure and manage the Windows 2003 cluster, the cluster-aware version of Exchange 2003 introduces new features and functionality not available with the Standard version of Exchange 2003.

Review the following list to learn more about the features and behavior of the Exchange 2003 cluster-aware version:

• Prerequisites Checking During installation of Exchange 2003 cluster-aware version, Exchange performs a prerequisite test to determine and validate that all requirements are met in the cluster before continuing the installation process.

• Shared Nothing Architecture With Exchange 2003, Windows clustering behaves in a Shared Nothing Architecture when nodes are in a cluster. In this behavior, nodes in the cluster can all access the same shared data; however, no node in the cluster can access the same data at the same time. What this means is, if node 1 of the cluster is accessed as a shared resource on a disk, node 2 cannot access the resource until node 1 is either manually taken offline or is failed over.

• Support for Eight Node Clusters Using Windows 2003 server clustering, organizations can build clusters with up to eight nodes.

• Kerberos Authentication Exchange 2003 clusters use Kerberos authentication to enhance security; it is enabled by default.

• Volume Mount Points New in Exchange 2003, support for volume mount points has been enabled for use with Windows 2003 clusters.

Planning Exchange 2000 Clusters

When planning clustering for Exchange Server 2003, there are several issues involving the network, software, storage, and load balancing that must be considered and planned.

Planning Network Resources

Exchange clusters require one TCP/IP address per virtual server in addition to the five TCP/IP addresses that were required to set up the Windows 2003 cluster environment. To run a 2-node Exchange cluster server in Active/Active mode, administrators are required to have two additional TCP/IP addresses to support the Exchange virtual servers. For example, a 2-node Active/Active cluster requires a total of seven static TCP/IP addresses.

Planning Cluster Disk Space

Storage space is another important factor when planning the Exchange cluster. As with the standard installation of any Exchange environment, administrators must consider the disk space requirements based on the expected growth of the Exchange server mailbox and data population.

To plan database drives and drive size requirements, calculate the expected size limit per mailbox and multiply the total by the number of expected mailboxes to calculate the disk space starting point. Also, factor in using deleted item retention, the company's growth rate, and the maximum number of mailboxes that will be supported on the cluster over its lifetime. To plan effectively, include an additional disk space in the final calculation to allow maintenance, unforeseen growth, and buffer space.

When planning drives to store Exchange server logs, plan enough disk space to support the overall operation of Exchange 2003. In addition, plan to include additional drive space for managing and maintaining logs, should backups be missed and files not flushed.

Software Requirements

To implement clustering technology with the Exchange Server 2003, administrators must use the Exchange Server 2003 Enterprise Edition. To install Exchange 2003 Enterprise in the cluster, administrators must install the installation files on the local disk of node in the cluster. For example, if administrators install the installation on node 1 in the C:\Exchsrvr directory, each node should also have the Exchange installation performed to C:\exchsrvr .

Load Balancing Mailboxes and Exchange Data

Load-balancing Exchange 2003 mailboxes and public folder information is important and can greatly improve the stability and performance of the Exchange 2003 cluster. When considering how to load-balance Exchange 2003 resources, it's up to the administrator to properly determine the total number of mailboxes per node in the cluster. Whether the cluster is configured for Active/Active or Active/Passive configuration, the bottom line is whether the surviving server will be able to handle the load should another server in the cluster be taken offline.

Validating Design Decisions and Testing

A front-end/back-end configuration can help reduce the load felt on the surviving node if there are a substantial number of Exchange 2003 server clients . Be sure to prototype cluster installations and configurations and execute detailed performance testing to calculate the most effective hardware and software configuration to support the load each node is expected to handle should the cluster fail over.

When load-testing to evaluate performance, perform tests on each node as it is online with other nodes at the same time. Validate functionality and performance and conduct the same set of tests on the cluster in a failover condition.