This is a 2-node Active/Active Cluster

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at]  

Topic Last Modified: 2006-04-28

The Microsoft® Exchange Server Analyzer Tool queries the Win32_Service Microsoft Windows® Management Instrumentation (WMI) class to determine the value of the Started key for ClusSvc, the Cluster service. A value of True indicates the Cluster service is running, and a value of False indicates it is not running.

The Exchange Server Analyzer also reads the following registry entry to determine the number of nodes in the cluster:

HKEY_LOCAL_MACHINE\Cluster\Nodes\<Node Number>\NodeName

The count of instances of NodeName represents the number of nodes in the cluster. In addition, the Exchange Server Analyzer reads the following registry entry to determine the number of Exchange Server resources in the cluster:

HKLM\Cluster\Resources\<Cluster Resource GUID>\Parameters\DestPath

The following resources on an Exchange Server cluster will have a DestPath value:

  • Microsoft Exchange Message Transfer Agent

  • Microsoft Exchange Information Store

The count of the instances of DestPath indicates the number of servers running Exchange Virtual Server (EVS) in the cluster.

If the Exchange Server Analyzer determines that there are 3 instances of DestPath in a cluster that has 2 instances of NodeName, a warning is displayed. This warning indicates that this is a two-node cluster with two servers running EVS, known as an Active/Active cluster.

  • In the Active/Active cluster model, the number of Exchange virtual servers in the cluster is equal to or greater than the number of physical nodes in the cluster.


Active/Active Exchange clusters can only be created in clusters made up of two nodes. If you have three or more nodes in your cluster, you must use the Active/Passive model.

  • In the Active/Passive cluster model, the number of Exchange virtual servers in the cluster is less than the number of physical nodes in the cluster.

Although Microsoft supports Active/Active clustering for Exchange Server, it is strongly recommended that Active/Passive implementations be used for Exchange clusters. Microsoft only supports Active/Active Exchange clusters that adhere to the following scaling limits:

  • The number of concurrent user connections per Exchange virtual server per physical node should never be greater than 1,900. If one node of the cluster is unavailable and if all Exchange virtual servers are online on a single node, the scaling limits remain at 3,800 connections for the two Exchange virtual servers. Because each user may make multiple connections, the number of mailboxes is not an accurate way to estimate the number of connections.

  • The average CPU utilization per Exchange store process should not be more than 40 percent. If the total CPU utilization by the STORE.EXE process on a node is more than 40 percent for a period of 10 minutes or more, you must move users to another Exchange virtual server or Exchange server. Note that this load does not include the CPU utilization consumed because of administrative tasks.

Migrating from an Active/Active cluster configuration to an Active/Passive configuration involves moving resources off the second EVS and then decommissioning it.

To migrate from an Active/Active cluster to an Active/Passive cluster

  1. Move the mailboxes hosted on the second EVS to the first EVS in the cluster. The first EVS in the cluster always contains the only Microsoft Exchange message transfer agent (MTA) resource in the cluster.

  2. After all of the mailboxes have been moved to the first EVS, take the second EVS offline.

  3. Remove the second EVS by doing one of the following:

    • On an Exchange Server 2003 cluster, right-click the Microsoft Exchange System Attendant resource and click Remove Exchange Virtual Server.

    • On an Exchange 2000 Server cluster, right-click the Microsoft Exchange System Attendant resource and click Delete.

  4. Verify that the EVS object has been removed from the Active Directory® directory service. Because of Cluster service account permission changes in Exchange Server 2003, your account must have permission to remove Active Directory objects.

  5. Take the remaining resources in the second EVS (for example, Physical Disk, Network Name, and IP Address) offline, and then delete them.

  6. Delete the resource group that contained the second EVS.

For more information about how to remove an EVS, see the section, "Removing an Exchange virtual server from a Cluster" in Deploying Microsoft Exchange 2000 Server Clusters Exchange (

For more information about best practices and recommendations for Exchange clusters, see the Exchange Server 2003 Deployment Guide (

For more information about deploying Exchange in a Windows server cluster, see the Microsoft Knowledge Base article 815180, "Considerations when deploying Exchange on an Active/Active cluster" (