Server clusters overview
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
Server clusters overview
A server cluster is a group of independent computer systems, known as nodes, working together as a single system to ensure that critical applications and resources remain available to clients. These nodes must be running Microsoft® Windows Server™ 2003, Enterprise Edition or Microsoft® Windows Server™ 2003, Datacenter Edition. Clustering allows users and administrators to access and manage the nodes as a single system rather than as separate computers. For more information about nodes, see Nodes.
A server cluster can consist of up to eight nodes and may be configured in one of three ways: as a single node server cluster, as a single quorum device server cluster, or as a majority node set server cluster. For more information about these three server cluster models, see Choosing a Cluster Model.
Every node may be attached to one or more cluster storage devices. For most versions of Windows Server 2003, Enterprise Edition or Windows Server 2003, Datacenter Edition, the choices for cluster storage include iSCSI, Serial Attached SCSI, parallel SCSI, and Fibre Channel. The following table provides details about the storage you can use with each version of the operating system, along with the maximum number of nodes you can have with each storage type:
| Description of Operating System | Storage | Maximum Nodes |
|---|---|---|
Windows Server 2003, Enterprise Edition, or Windows Server 2003, Datacenter Edition Versions:
Platforms:
|
Parallel SCSI |
2 |
Windows Server 2003, Enterprise Edition, or Windows Server 2003, Datacenter Edition Versions:
Platforms:
|
Fibre Channel |
8 |
Windows Server 2003, Enterprise Edition, or Windows Server 2003, Datacenter Edition Versions:
Platforms:
|
iSCSI or Serial Attached SCSI (SAS) |
8 |
The following figure shows a four-node cluster that provides high availability for four different types of applications or services:
.gif "4-node server cluster")
A server cluster runs several pieces of software that fall into two categories: the software that makes the cluster run (clustering software) and the software that you use to administer the cluster (administrative software). By default, all clustering and administration software files are automatically installed on your computer when you install any operating system in the Microsoft® Windows Server 2003 family of products.
Important
- Only computers running Windows Server 2003, Enterprise Edition or Windows Server 2003, Datacenter Edition can be cluster nodes.
Clustering software
The clustering software enables the nodes of a cluster to exchange specific messages that trigger the transfer of resource operations at the appropriate times. There are two main pieces of clustering software: the Resource Monitor and the Cluster service. The Resource Monitor facilitates communication between the Cluster service and application resources. The Cluster service runs on each node in the cluster and controls cluster activity, communication between cluster nodes, and failure operations. When a node or application in the cluster fails, the Cluster service responds by restarting the failed application or dispersing the work from the failed system to the remaining nodes in the cluster. For more information about this process, see Failover and failback.
Administrative software
Administrators use cluster management applications to configure, control, and monitor clusters. The Windows Server 2003 family provides Cluster Administrator for this purpose. Any computer running Microsoft Windows NT® version 4.0 Service Pack 3 or later, regardless of whether it is a cluster node, can install Cluster Administrator. By default, a copy of Cluster Administrator is automatically installed on your computer when you install Microsoft® Windows Server® 2003, Standard Edition; Windows Server 2003, Enterprise Edition; or Windows Server 2003, Datacenter Edition. For information about remote administration, see Installing Cluster Administrator on a remote computer.
You can also create, configure, and administer clusters using the cluster command. For more information, see Administering Server Clusters. You can use or create custom administration tools developed using the Cluster automation interfaces. For more information about the Cluster automation interfaces, see the Microsoft Platform Software Development Kit (SDK), available separately.
Administrators organize cluster resources into functional units, called groups, and assign these groups to individual nodes. If a node fails, the Cluster service transfers the groups that were being hosted by the node to other nodes in the cluster. This transfer process is called failover. The reverse process, failback, occurs when the failed node becomes active again, and the groups that were failed over to other nodes are transferred back to the original node. For more information about resources, see Server Cluster Resources. For more information about groups, see Server Cluster groups.