Common Exchange 2003 Cluster Questions – Original Posted May 1, 2005

Whenever I teach Exchange Server 2003 classes, I get to the module that discusses clustering and I want to scream. There just isn’t enough material to discuss Exchange clustering properly. Anyways, I started talking more and more about clustering as there seems to be a great deal of interest in clustering Exchange in many organizations. So, here are some of the more common questions I get when discussing Exchange Server Clustering.


Q1. If I have two nodes in the cluster, do the mailboxes exist on both nodes?

A1. Microsoft Server Clustering uses a shared nothing architecture. In this architecture, resources are created for a virtual server (they include any needed Physical Disk resources, Network Name, IP Address, and services). In the case of Exchange, the cluster virtual server is built and all the resources run on the active node. If the virtual server fails over or is moved to the passive node, the second node in the cluster then takes control of all of those resources. So, short answer: The mailboxes exist in the storage group associated with the physical disk resource and this disk resource is passed back and forth between the nodes. Only one copy of each mailbox exists.


Q2. If I build a two node cluster, do the computers have to be exactly the same?

A2. No, they don’t need to be exactly the same, but they need to be very close in order to be supported. See KB 814607 and read the section on Server Cluster Qualification for more information.


Q3. I read the book and I also heard you say that you will often need additional single machine Exchange servers when using Exchange Server Clusters. Why do I need to have Exchange servers that are not part of a cluster?

A3. Several different services are not properly supported in a cluster and others just simply do not work. These services include:

  • Active Directory Connector
  • Intelligent Message Filter
  • Site Replication Service
  • Internet Mail Wizard
  • /DisasterRecovery setup switch
  • Lotus Notes Connector
  • Novell GroupWise Connector
  • Exchange Events

To top it off, because of the SRS and ADC issues, an Exchange Server 2003 cluster can’t be the first Exchange Server 2003 server in an Exchange 5.5 site. Thanks to David Elfassy for helping me with this list.!1pvwhiXzZoTl_cUJCU1PSHfw!185.entry


Q4. MSDTC is required as part of the cluster install and there are conflicting articles on the Microsoft site about whether it needs its own cluster group with its own IP resource, network name resource, and physical disk resource. What is the right answer?

A4. MSDTC does not require its own physical disk resource and it can be included in the default cluster group. You can get more info on my blog under the Micrososft Clustering category.


Q5. What is wrong with using Active/Active for Exchange clustering vs. Active/Passive?

A5. Auggghhh. Read my blog here for the answer(Summary – Don’t use Active/Active):!1pwuGkyvTDx37q1_Y3JQ_E6g!137.entry


Q6. How do I add the IMAP4 and POP3 services to my Exchange cluster after it is installed?

A6. It is covered here: but to boil it down to the basics, the steps (shown for IMAP4 only) are:

  1. In the Cluster Group for the Exchange Virtual Server (EVS), right click it and select New, Resource, then enter the name (i.e. EVS1 IMAP4)
  2. Select Microsoft Exchange IMAP4 Server Instance from the Resource Type list.
  3. Add all nodes as possible owners
  4. Add the System Attendent as a dependency


Q7. Why do I need MSDTC to be installed in order to build an Exchange cluster?

A7. Because. It is really only needed during the installation of the cluster because the Exchange install application needs the cdowfevt.dll that is part of the Com+ installation. MSDTC is used for workflow applications in Exchange, but other than that, it isn’t used at all after the install. Oops, I take it back, it is used for upgrading as well.


Q8. How many physical disk resources should I plan for an Exchange cluster?

A8. At a minimum, you should have 4 physical disk resources per EVS, 5 if you the MTA is heavily used as it should have its own physical disk resource.

  • One for the quorum and MSDTC (yes, you can put the MSDTC on the same disk without any trouble)
  • One for the store (one for each storage group at a minimum, I prefer one for each store)
  • One for the transaction logs (on for each storage group)
  • One for SMTP
  • One for the MTA (possibly… it depends how much the MTA will be used in your environment)

Keep in mind that each of these disks should be a LUN on a SAN. If you are carving them up yourself, I highly recommend using RAID 1 sets for the transaction logs, SMTP, and MTA (if you use it heavily) and RAID 5 for the mailbox stores. Do not create physical disk resources that are partitions on the same physical drives. When it comes to disk sizing, I highly recommend reading Nicole Allen’s blog entry at She does a fantastic job of explaining how to size disks for Exchange. You can also see similar information on storage optimization at


Q9. Why do you recommend MSCS for the mailbox servers but not for the OWA servers?

A9. The OWA (also known as the Front End or FE) servers do not have a requirement for shared disk storage. You can achieve server redundancy and horizontal scaling using NLB or hardware load balancers with multiple FE servers since there is no requirement for a database or information stores on an FE.


Q10. Windows Server 2003, Enterprise Edition, support eight nodes in a cluster. Can I have eight virtual Exchange servers?

A10. While you can have up to eight nodes in a cluster, you can’t have that many Exchange Virtual Servers in a single cluster. Once you go to three or more nodes, Exchange forces you to have at least one passive node. So, for eight nodes, it is possible to have only up to seven active nodes and one passive node. There are a couple of concerns that you need to be aware of when creating larger than two node Exchange clusters.

  • If you have three or more nodes, each node can only host a single EVS. If, for example, you have three nodes with two active nodes and one passive node(Active/Active/Passive), and one of the active nodes failes, it will failover to the one passive node. If the other EVS failed, then the EVS would not failover to another node. It would just fail. While you can potentially have two EVSs on the same node in an Active/Active two node cluster, you can’t have two EVSs on the same node in larger clusters.
  • In a large cluster, it makes sense to have two or more passive nodes so that you can support more than one failure at a time.
  • My personal recommendation is to never go beyond 4 nodes (Active/Active/Active/Passive) as you will be fighting disk letter issues (think about 5 or more physical disk resources per EVS and then do the math), and it would become very complicated to monitor and manage. With three EVSs, the number of disk drive letters gets to be pretty high and will make it difficult to add new physical disk resources and do to things like disk migrations in the future. Yes, you can use mount points, but using disk letters makes it easier to manage.


Q11. How many IP address do I need for an Exchange cluster?

A11. You need IP address for:

  • NodeA Public Interface
  • NodeA Private Interface (for heart beat)
  • NodeB Public Interface
  • NodeB Private Interface (for heart beat)
  • Default Cluster Group (IP is needed as dependency for network name resource)
  • Exchange Virtual Server (IP is needed as dependency for network name resource for your EVS). You will need one IP for each EVS in your cluster.
  • MSDTC cluster group (if you break it out into its own cluster group, it will need an IP resource, but thisis  not needed)

Remember a couple of important things regarding your heart beat networks:

Note: I will return and update this entry as I think of the more common questions that I get in my Exchange classes.

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