How to implement Exchange 2000 Server on a Windows 2000-based cluster

This step-by-step article describes the implementation of Exchange on a Microsoft Windows 2000-based cluster.

Although other information is available about Windows 2000-based clusters, this article describes server clustering from the Exchange viewpoint.

Exchange Clustering Overview

When you install Microsoft Exchange 2000 Server on a Windows cluster, it is configured as a virtual server. It runs as a virtual computer that can be passed between cluster nodes. Exchange clients are unaware of this, and only have to connect their Microsoft Outlook profiles to the name of the Exchange virtual server.

Clustering technology makes it possible for you to design high-availability solutions for enterprise-level programs. This is especially desirable for mailbox and public folder servers. However, clusters that are based on the Windows 2000 Cluster service are different from load-balancing clusters. Load-balancing clusters are suitable for Exchange front-end (FE) servers that do not store any user data. Clusters that are based on the Windows 2000 Cluster service rely on completely different mechanisms. They are suitable for Exchange back-end (BE) servers that host the user data. The Cluster service is available only in Windows 2000 Advanced Server and Windows 2000 Datacenter Server. Note that only the Enterprise Edition of Exchange 2000 Server supports this form of clustering.

For additional information about the Microsoft Cluster Service (MSCS), see the "REFERENCES" section of this article.

Install Exchange on a Cluster

When you install Exchange on a cluster node, the Exchange Setup program copies the program files to the local disk of the cluster node. If you have a cluster with two nodes such as Node A and Node B, Setup copies the Exchange program files to the hard disk of Node A. For example, this might be drive C of Node A. Setup makes no changes to Active Directory at this time. You then run Setup a second time to install the Exchange program files on the local hard disk of the second node. For example, this might be drive C of Node B.

After the Exchange program files are copied to the hard disks of each node, you must configure a "Group" for the Exchange resources. A "Group" in this case is defined as a logical container that holds resources for a virtual server. This Exchange virtual server will have many of the same resources that all physical Exchange servers have such as:

• A host name
• An IP address
• Disk storage

After you create these resources, you must configure resources that reflect the Exchange services. For example, an Exchange System Attendant resource, an Exchange Information Store resource, and other resources. These resources can be either taken offline, which mimics the stopping of the particular service, or brought online, which mimics the starting of the particular service. You can also change the current resource owner (the cluster node). For example, you can configure Node B to run this resource instead of Node A.

The Microsoft System Attendant resource is the only resource that you must manually create. The other Exchange service-related resources are automatically created after you create the System Attendant resource. It is at this time that changes are written to Active Directory and an object for this Exchange-based server is listed in the Servers container for your administrative group.

Exchange supports two different configurations of virtual servers, Active/Passive and Active/Active. For additional information about the installation of Exchange, see the "REFERENCES" section of this article.

Active/Passive Clusters

Active/Passive clustering is supported by Exchange Server 5.5 and later. In an Active/Passive cluster, the following configuration exists:

• At least two nodes. For example, Node A and Node B.
• One shared disk system, the ownership of which can be moved between cluster nodes.
• One IP address that is created in the Exchange "group."
• One network name that is created in the Exchange "group."
• One virtual Exchange server. Both nodes can own this virtual Exchange server, but only one node can own the virtual Exchange server at a time.

In an Active/Passive cluster, clients connect to an Exchange virtual server that is currently owned by one node of the cluster. For example, this might be Node A. In this case, Node A has control over the shared disk system that contains the Exchange databases. If Node A experiences a hardware failure and goes offline, the other node in the cluster (Node B) detects this and takes ownership of the virtual Exchange server and all its associated resources. These resources include the network name, IP address, the shared disk system, the Exchange System Attendant, and other resources. This process occurs without the currently-logged-on users knowledge. Because the clients connect to a virtual Exchange server, they are unaware of the fact that the physical server has changed. After the offline node (Node A) is restored to service, the virtual Exchange server can be moved back to it.

Active/Active Clusters

Active/Active clustering is supported by Exchange 2000 Server and later. However, this form of clustering is not supported in earlier versions of Exchange Server. In an Active/Active cluster, you have multiple virtual Exchange Servers instead of only one virtual Exchange server on an Active/Passive cluster. Both of the virtual Exchange servers can be moved between the different nodes of the cluster, or both virtual Exchange servers can simultaneously run on one node. In an Active/Active cluster, the following configuration typically exists:

• At least two nodes. For example, Node A and Node B.
• Two shared disk systems, the ownership of which can be moved between the cluster nodes.
• Two IP address that are created in two separate Exchange "groups."
• Two network names that are created in two separate Exchange "groups."
• Two virtual Exchange servers. Both nodes can own these virtual servers and both virtual Exchange servers can run on either of the nodes, but only one node can own each virtual Exchange server at a particular time.

In most cases, each virtual Exchange server is running on a separate node. For example, one virtual Exchange server would run on Node A, and one virtual Exchange server would run on Node B.

In the case of a hardware failure or where one node is taken offline, the other node detects this, and then takes ownership of the whole Exchange group that was running on the first node. This is known as a "failover." In the case of a two-node cluster such as Node A and Node B, the second node (Node B) would then host two virtual Exchange servers. In this example, Node B would have ownership of both shared disk systems, both IP addresses, both network names, and both virtual Exchange servers. The connected Exchange clients are unaware of this process.

When the first node (Node A) is brought back online, the virtual Exchange server that "failed over" to the second node can be moved back to its original node. This process is known as "failback."

NOTE: Exchange 2000 Server on Windows 2000 Datacenter Server is supported in an Active/Active cluster only in a two-node configuration. Active/Passive clustering on Windows 2000 Datacenter Server has the following configuration:

• Active/Active/Active/Passive

In this configuration, one cluster node is passive and is available to host an Exchange virtual server if a failover occurs. As of October 2002, a cluster with four active nodes is not supported.

Exchange 2000 Enterprise Server also supports a maximum of four storage groups with five databases for each storage group. This limitation also applies to a clustered node. Because of this, you must make sure that if all nodes fail except for one, the total number of storage groups on the remaining node does not become more than 4, and that the total number of databases does not become more than 20. For example, in a two-node Active/Active cluster, two virtual Exchange servers each with three storage groups would experience a problem at failover, because the remaining node would have to host 6 storage groups, and this is over the limit.

Active/Passive Compared to Active/Active Clusters

There are advantages and disadvantages to both Active/Passive and Active/Active clustering. Microsoft recommends that you use Active/Passive cluster configurations because they are highly scaleable and they have less administrative overhead than Active/Active clusters.

The advantage of an Active/Active over Active/Passive clustering is that both nodes in the Active/Active cluster work at the same time. However, because an Active/Active cluster can support only 1,900 MAPI clients per node, and because of the increased administrative overhead you must perform to maintain the cluster, this advantage may not occur in a real-world scenario. For example, increased administrative overhead includes monitoring for virtual memory fragmentation.

The Active/Passive cluster configuration has less administrative overhead, is more scaleable than an Active/Active configuration, and because the Active/Passive cluster can host more users, it also has a financial advantage.

NOTE: While the hosting of public folders is supported in a clustered environment, it may not make financial sense to do so because you can easily replicate public folders between the Exchange servers in your organization. However, because mailboxes cannot be replicated, it is important to host Exchange servers on which mailboxes are stored in a clustered environment.

Exchange Components Supported in a Clustered Environment

Not all Exchange components work in a clustered environment. The following lists describe the Exchange components that are supported in a clustered environment:

On an Active/Passive Cluster

• The Microsoft Exchange System Attendant.
• The Microsoft Exchange Information Store.
• The following protocols:
  • POP3
  • IMAP
  • SMTP
  • HTTP
• Full-text indexing.
• Message Transfer Agent (MTA).

On an Active/Active Cluster

• The Microsoft Exchange System Attendant.
• The Microsoft Exchange Information Store.
• The following protocols:
  • POP3
  • IMAP
  • SMTP
  • HTTP
• Full-text indexing.
• Message Transfer Agent (MTA).
  
  NOTE: The MTA resource is an Active/Passive cluster resource. There can only be one MTA resource per cluster. In the case of an Active/Active cluster, only one virtual Exchange server will have the MTA resource.

Unsupported Components

The following Exchange resources are not supported in a clustered environment:

• Network News Transfer Protocol (NNTP)
• Key Management Server (KMS)
• Instant Messaging (IM)
• Chat
• Connectors to the following messaging systems:
  • Novell GroupWise
  • Lotus Notes
  • Lotus cc:Mail
  • Microsoft Mail
  • IBM OV/VM (PROFS)
  • SNADS
• The Microsoft Exchange Event
• The Site Replication Service (SRS)

For additional information about Exchange components that are supported in a clustered environment, click the following article number to view the article in the Microsoft Knowledge Base:

Troubleshooting

When Exchange is hosted on a Cluster service computer, you must perform some common Exchange tasks differently than if Exchange is installed in a non-clustered environment.

• Exchange 2000 Server Setup
  Before you install Exchange 2000 Server on a cluster server, see the C20_clustering.rtf document that is stored in the DOCS folder on the Exchange 2000 Server CD-ROM.
• The Eseutil utility
  You must give special consideration when you run the Eseutil database integrity utility with the /CC switch. For additional information about this issue, click the following article number to view the article in the Microsoft Knowledge Base:
  266689  (http://support.microsoft.com/kb/266689/ ) The 'ESEUTIL /CC' command does not work on cluster server
• Adding additional Exchange virtual servers For additional information about this issue, click the following article number to view the article in the Microsoft Knowledge Base:
  293510  (http://support.microsoft.com/kb/293510/ ) How to add an Exchange 2000 virtual server to a cluster server
• Installing hotfixes or service packs
  Read the README file that is included with the update before you install a hotfix or service pack on a cluster server. In most cases, the passive node of the cluster is updated first. The virtual servers are then moved to the passive node, and then the other node is updated.
• Exchange database restoration
  For information about disaster recovery for Exchange 2000, visit the following Microsoft Web site:
  http://www.microsoft.com/technet/prodtechnol/exchange/2000/library/disrec00.mspx (http://www.microsoft.com/technet/prodtechnol/exchange/2000/library/disrec00.mspx)

For additional information about related topics, click the following article numbers to view the articles in the Microsoft Knowledge Base: For additional information about related topics, visit the following Microsoft Web sites: