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Server Clusters

Updated: April 10, 2006

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Server clusters

A server cluster is a group of independent computer systems, known as nodes, running Microsoft® Windows Server™ 2003, Enterprise Edition or Microsoft® Windows Server™ 2003, Datacenter Edition, and working together as a single system to ensure that critical applications and resources remain available to clients. The nodes in a cluster remain in constant communication through the exchange of periodic messages, called heartbeats. If one of the nodes becomes unavailable as a result of failure or maintenance, another node immediately begins providing service (a process known as failover).

Server clusters can combine up to eight nodes. In addition, a cluster cannot be made up of nodes running both Windows Server 2003, Enterprise Edition and Windows Server 2003, Datacenter Edition since the different operating systems may be running incompatible versions of the Cluster service. In server clusters with more than two nodes, all nodes must run Windows Server 2003, Enterprise Edition or Windows Server 2003, Datacenter Edition, but not both. However, a server cluster can be operated with some nodes running the Microsoft® Windows® 2000 operating system and others running Windows Server 2003, Enterprise Edition or Windows Server 2003, Datacenter Edition.

Server clusters can be set up as one of three different cluster model configurations:

  • Single node server clusters can be configured with, or without, external cluster storage devices. For single node clusters without an external cluster storage device, the local disk is configured as the cluster storage device.

  • Single quorum device server clusters have two or more nodes and are configured so that every node is attached to one or more cluster storage devices. The cluster configuration data is stored on a single cluster storage device.

  • Majority node set server clusters have two or more nodes but the nodes may or may not be attached to one or more cluster storage devices. The cluster configuration data is stored on multiple disks across the cluster and the Cluster service makes sure that this data is kept consistent across the different disks.

It is recommended that you understand the advantages and limitations of the different cluster models before you configure your server cluster. For example, a majority node set cluster can tolerate fewer simultaneous node failures than an equivalent single quorum device cluster.

For more information about the three cluster models, see Choosing a Cluster Model.

For cluster storage, you can use parallel SCSI, Fibre Channel, Serial Attach SCSI (SAS), or iSCSI. For details about which types of storage can be used with a specific Windows Server 2003 operating system, see Server clusters overview.

Server clusters enable users and administrators to access and manage the nodes as a single system rather than as separate computers.

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