Example of Fault Tolerant Exchange 2003 Topologies


Topic Last Modified: 2005-05-25

This section provides examples of Exchange 2003 topologies, including estimated availability percentages. To maximize your understanding of the availability percentages presented in this section, read "Determining Availability Requirements" in Quantifying Availability and Scalability Requirements and Establishing a Service Level Agreement.

Although the topologies described in this section are simplified, they can help you understand how to implement fault tolerant measures in your messaging infrastructure.

The tiers and estimated availability levels in this section are arbitrary and are not intended to reflect any industry-wide standards.
Actual availability levels depend on many variables. Therefore, before you deploy your Exchange 2003 topology in a production environment, it is recommended that you test the deployment in both a laboratory test and a pilot deployment setting.

The topologies represented in this section range from a first-tier to a fifth-tier messaging system. All of the tiers are based on a first-tier topology, which includes the following components:

  • Mid-level server-class hardware in all servers

  • Single-server advanced firewall solution

  • Single domain controller that is also configured as a global catalog server

  • Single server that is running Domain Name System (DNS)

  • Exchange 2003 and Windows Server 2003 correctly configured

First-tier messaging system


The following table includes a description of the five possible tiers, as well as the estimated availability levels of each.

Tier descriptions and estimated availability levels

Tier description Estimated availability level

First-tier messaging system   For the description of a first-tier messaging system, see Figure 3.2 and the preceding bulleted list.

99% or higher

Second-tier messaging system   A second-tier system meets the requirements of a first-tier system, but also includes multiple domain controllers, multiple DNS servers, a separate monitoring server, and an entry-level redundant array of independent disks (RAID) storage solution that is not on a SAN.

99.5% or higher

Third-tier messaging system   A third-tier messaging system meets the requirements of the second-tier system, but also includes a mid-range RAID storage solution using a SAN, and Network Load Balancing (NLB) implemented on Exchange front-end servers.

99.9% or higher

Fourth-tier messaging system   A fourth-tier message system meets the requirements of the third-tier system, but also includes a high-range RAID storage solution, a high-range SAN solution, back up and restore using Volume Shadow Copy service, and active/passive Microsoft Windows® Clustering (with multiple passive nodes), for all back-end Exchange servers.

99.99% or higher

Fifth-tier messaging system   A fifth-tier messaging system meets the requirements of the fourth-tier system, but also includes complete site failover (in the event of a site failure) through the use of a multi-site design that includes a geographically dispersed clustering solution.

99.999% or higher