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Exchange Clustering Basics

Nirmal Sharma [Microsoft MVP, MCSEx3]

Nirmal Sharma [Microsoft MVP, MCSEx3] Photo

Nirmal is a Microsoft MVP in Directory Service. He has been involved in Microsoft Technologies since 1994 and followed the progression of Microsoft Operating System and software. He is specialised in writing “internal” technical articles, white papers and tips on various Microsoft technologies.

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What is Clustering? How do I cluster Exchange? Which components make up an Exchange Cluster? Today we answer these questions and more to kick start those new to this technology.

How to cluster Exchange Server 2000/2003/2007?

Clustering Exchange 2007 Services is an easy task provided you have configured the Clustering Software (MSCS) on the Operating System. Clustering Exchange 2000 and 2003 require some manual efforts. In this case, you need to create a few resources manually. These resources are created automatically in case of Exchange 2007. I will walk you through the steps to create an Exchange Cluster.

There are four steps to be performed to cluster Exchange Server 2000/2003:

  • Prepare Active Directory to support Exchange 2000/2003
  • Install and Configure the Clustering Service
  • Install Exchange on each node one by one
  • Create the Exchange Virtual Server cluster resource

1. Prepare Active Directory to support Exchange 2000/2003

As with non-clustered installations Active Directory and the domain need to be Preped. In this step you will run the following commands:
Setup /ForestPrep
Setup /DomainPrep

2. Install and Configure the Clustering Service

Following ForestPrep and DomainPrep, you need to prepare the clustering service on each node. If you have two nodes, both must join the cluster and a cluster group must be created.

Please refer to this article at Microsoft site to install the Clustering Software

Secondly you need to enable the services required by Exchange. This.NET FrameWork, ASP.NET, and IIS must be enabled and started depending on the Operating System on which you're going to install the Exchange.

In addition to the standard requirements, the Microsoft Distributed Transaction Coordinator (MSDTC) is required for clustering Exchange. This resource must be created separately before executing the Exchange installation.

To install MSDTC in Windows 2000 Server, use ComClust.exe.

To install MSDTC in Windows 2003 Server, create a resource in the clustering software.

For more information on how to install MSDTC, please use the below link as a reference for the steps:

Note: MSDTC resource must be running before running the Exchange Installation. MSDTC resource should exist in the Default Cluster Group and must be configured properly using the above mentioned link.

3. Install Exchange on each node one by one

In this step you will execute the Exchange Setup on each node. Few points to summarize:

  • You need to run the Exchange Setup from the CD on each node one by one. It is not advisable to run the Exchange Setup concurrently on more than one node at a time.

  • Make sure the drive letter you use to install the Exchange binaries is the same on each node. It must "not" be the "shared drive" (LUN) from the storage.

4. Create the Exchange Virtual Server cluster resource

On completing the Exchange binary files installation on all nodes, we need to create one or more Exchange Virtual Server cluster resources. For example in a 2 node Active/Passive cluster a single EVS would be created. In a 4 node cluster where 3 are active and 1 is passive, 3 EVSs would be created.

Here are the steps to be followed for each of the EVSs:

  • For each EVS create an EVS cluster Group
  • Create an IP Address resource
  • Create a Network Name resource
  • Move a Disk resource to the EVS cluster group
  • Create an Exchange System Attendant resource

Note: To create any additional EVSs, you need to perform the above steps by creating a separate EVS cluster group.

In Exchange Server 2007, you don't need to create the EVS resources manually. This is done by the Exchange Setup automatically.

Exchange Clustering Facts

Here are some requirements, best practices and known facts about Exchange Server clustering:


  1. Make sure you are running a DNS Server in the environment and that it accepts dynamic updates. The Exchange Setup will register the Network Name and IP Address associated with it at the DNS Server. Otherwise Exchange will not function:

  2. All cluster nodes must be member of a single domain. Exchange 2003 Clusters are also not supported on computers that are domain controllers.

  3. Make sure a sufficient number of Static IP Addresses for each Exchange Cluster are available.

  4. Clustering Software must be installed and configure before running the Exchange Setup. Otherwise Exchange will not install its cluster-aware components.

  5. Before proceeding with the Exchange Installation make sure the disks are empty.

Best Practices

  1. Use identical hardware across the cluster nodes for Exchange Clustering - this is just a recommendation.

  2. The stability of Exchange Resources is greatly improved in Windows Server 2003. If possible, always use Windows Server 2003 with Exchange Server 2003.

  3. Start Exchange Server installation one by one on each node. Do not run installations on multiple nodes at the same time.

  4. You must install the same Exchange version on each node. The Exchange binaries have to be installed on the local drive.

  5. For cluster node communications, create a user account that is a member of the Local Administrators group. Best practices say that you create a domain user account and add it to the Local Administrators group of all the nodes.

  6. Always create the MSDTC resource in the Default Cluster Group which is created when you install the Clustering Software.

  7. Before running Exchange Setup on a cluster node, make sure the node is not holding any resources. It is always advisable to move the resources to another node in the cluster.

Known Facts and Limitations

  1. More than 50% of the issues with clustering are because of non-certified hardware and applications running on the Operating System.

  2. The dependency of the resources has been changed in Exchange 2003 clustering. Hence, the failover time has been improved in the Exchange 2003 clustering over Exchange 2000.

  3. Any given EVS can run only on one node at a time. You can not have multiple instances of the same EVS.

  4. Not all Exchange services are supported in a cluster. Only the following services are:
    System Attendant
    Information Store
    Routing Engine
    POP3, IMAP4, SMTP, and HTTP
    MS Search (by default)

  5. Clients communicate with the Exchange Cluster using its EVS IP.

  6. In Exchange Server 2000 and 2003, you need to create the System Attendant Resource manually in the Cluster Administrator but in Exchange 2007, all Exchange Resources are created automatically during setup.

  7. If you installed Exchange Server before configuring the clustering software then you must uninstall Exchange Server, configure the Clustering Service and then install the Exchange Server.

  8. Site Replication Service is not supported in cluster environment.

  9. Exchange Clustering requires either Enterprise or Datacenter editions depending on the requirement of the number of nodes. The number of nodes is summarized below:
    Windows 2000 Advanced Server - 2 nodes
    Windows 2000 Datacenter Server - 4 nodes
    Windows 2003 Advanced Server - 8 nodes
    Windows 2003 Datacenter Server - 8 nodes

  10. Exchange Disks must be configured as Basic Disks. Dynamic Disks are not supported.

  11. Unattended is not supported when installing Exchange Server in a cluster environment. You have to visit each node individually and then execute the setup from there.

  12. For security reasons, when creating Exchange Virtual Server in the cluster, the Windows IMAP4 and POP3 services are no longer enabled by default on Windows Server 2003. These resources are not created on servers running Windows Server 2000. If you want to add these resources, please follow the guide here:

  13. When you create the Exchange System Attendant cluster resource, this automatically creates the following resources:
    Exchange Information Store Instance
    Exchange Message Transfer Agent instance
    Exchange Routing Service Instance
    SMTP Virtual Server Instance
    Exchange HTTP Virtual Serve Instance
    Exchange MS Search Instance

  14. The Message Transfer Agent resource is created only once in the cluster when you add the first Exchange Virtual Server. The same instance is not created but is shared by other EVS in the cluster.


Today we went through the basics of the Exchange Clustering. We saw how clustering works and what is required to cluster Exchange. Finally we went through some recommendations, best practices and limitations of the Exchange Server in a cluster environment.

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