Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1, Exchange Server 2007
Topic Last Modified: 2007-11-21

A single copy cluster (SCC) is a clustered mailbox server that uses shared storage in a failover cluster configuration to allow multiple servers to manage a single copy of the storage groups. This feature is similar to the clustering features in previous versions of Microsoft Exchange. However, there are some significant changes and improvements that have been made. The way in which you build, manage, and troubleshoot an SCC is completely different from the way in which previous versions of Exchange clusters were built and managed. In addition, the out-of-box failover behavior has changed significantly in Microsoft Exchange Server 2007.

These changes and improvements include:

As illustrated in the following figure, SCCs require the use of a shared-nothing architecture, which includes shared disk storage. In a shared-nothing architecture, although all nodes in the cluster can access shared data, they cannot access it at the same time. For example, if a physical disk resource is assigned to node 1 of a two-node cluster, node 2 cannot access the disk resource until node 1 is taken offline, fails, or the disk resource is moved to node 2 manually.

Single Copy Cluster Architecture

In an SCC, an Exchange 2007 Mailbox server uses its own network identity, not the identity of any node in the cluster. This network identity is referred to as a clustered mailbox server. If the node running a clustered mailbox server experiences problems, the clustered mailbox server goes offline for a brief period until another node takes control of the clustered mailbox server and brings it online. This process is known as failover. The storage hosting the clustered mailbox server's storage groups and databases is hosted on shared storage that is available to each possible host node of the clustered mailbox server. As the failover occurs, the storage associated with the clustered mailbox server is logically detected from the failed node and placed under the control of the new host node of the clustered mailbox server.

In addition to failover, an administrator can manually move a clustered mailbox server between nodes in a cluster. This process is known as a handoff. A handoff should only be performed using the Move-ClusteredMailboxServer cmdlet in the Exchange Management Shell, or, if running Exchange 2007 SP1, by using the Manage Clustered Mailbox Server wizard in the Exchange Management Console.

Cluster Administrator and Cluster.exe provide mechanisms for moving resource groups between nodes in a cluster. When performing a handoff of a clustered mailbox server in an SCC, we recommend that you use the Move-ClusteredMailboxServer cmdlet or the Manage Clustered Mailbox Server wizard instead of using the cluster management tools because both the cmdlet and the wizard enable the administrator to specify a reason for the handoff.

Windows Failover Cluster

To create an SCC for Exchange 2007, you must create a failover cluster using the Cluster service. Failover clustering is included in Windows Server 2003 Enterprise and Datacenter Edition and Windows Server 2008 Enterprise and Datacenter operating systems. In both operating systems, the Cluster service is the essential software component that controls all aspects of clustered resources. When Exchange 2007 Setup is run on a node of a failover cluster, the cluster-aware version of Exchange is automatically installed. A clustered mailbox server in an SCC environment contains the following elements:

  • Shared storage   Exchange 2007 supports both shared storage and non-shared storage clusters. SCCs use shared storage. For more information about non-shared storage Exchange clusters, see Cluster Continuous Replication.

  • Resource DLL   Windows communicates with resources in a cluster by using a resource dynamic-link library (DLL). Exchange 2007 provides its own custom resource DLL (named Exres.dll) to communicate with the Cluster service. Communication between the Cluster service and Exchange 2007 is customized to provide cluster functionality, including failover.

  • Groups    Exchange 2007 uses Windows cluster groups to contain and represent a clustered mailbox server. In an SCC, a clustered mailbox server is a cluster group containing clustered Exchange resources, such as an IP address, one or more physical disk resources, the Microsoft Exchange System Attendant service, and other Exchange resources.

  • Resources   Clustered mailbox servers include resources, such as IP Address resources, Network Name resources, and physical disk resources. Clustered mailbox servers also include their own Exchange-specific resources. When creating a clustered mailbox server, Exchange automatically creates the other essential Exchange-related resources, such as the Microsoft Exchange System Attendant service, the Microsoft Exchange Information Store service, and one or more Microsoft Exchange storage group or database instances.

Deploying Single Copy Clusters

Deploying an SCC is similar to deploying a stand-alone Exchange server, and it is similar to deploying cluster continuous replication (CCR). However, there are some significant differences to be aware of when deploying SCCs. We recommend that you review the following topics:

Basic architecture of an SCC