Failover Clustering

Failover clustering in Microsoft SQL Server 2005 provides high-availability support for an entire SQL Server instance. For example, you can configure a SQL Server instance on one node of a failover cluster to fail over to any other node in the cluster during a hardware failure, operating system failure, or a planned upgrade.

A failover cluster is a combination of one or more nodes (servers) with two or more shared disks, known as a resource group. The combination of a resource group, along with its network name, and an internet protocol (IP) address that makes up the clustered application or server, is referred to as a failover cluster or a failover cluster instance. A SQL Server failover cluster appears on the network as if it were a single computer, but has functionality that provides failover from one node to another if the current node becomes unavailable. A failover cluster appears on the network as a normal application or single computer, but it has additional functionality that increases its availability.

When to Use Failover Clustering

Use failover clustering to:

Installing Failover Clustering

To use failover clustering, you must follow specific installation steps.

To install, configure, and maintain a SQL Server failover cluster, use SQL Server Setup. You can also use Setup to upgrade an existing 32-bit instance of SQL Server 7.0 or Microsoft SQL Server 2000 to a SQL Server 2005 failover cluster. For more information, see Version and Edition Upgrades.

Use SQL Server Setup in a failover cluster to:

  • Install SQL Server on multiple nodes in a failover cluster. You are limited only by the number of nodes supported by the operating system.
    Before installing failover clustering, you must ensure that your system meets minimum requirements, and configure the Microsoft Cluster Service (MSCS). For more information on specific requirements for a failover cluster, see Hardware and Software Requirements for Installing SQL Server 2005 and Before Installing Failover Clustering.
    All nodes in a failover cluster must be of the same platform, either 32-bit or 64-bit. Furthermore, 64-bit SQL Server editions must be installed on 64-bit hardware running the 64-bit versions of Microsoft Windows operating systems. For more information, see Hardware and Software Requirements for Installing SQL Server 2005.
  • To install a Microsoft SQL Server 2005 failover cluster, you must create and configure a failover cluster by running SQL Server Setup. For more information, see Installing a Failover Cluster.
  • Add or remove nodes from a failover cluster configuration without affecting the other cluster nodes. For more information, see Maintaining a Failover Cluster.
  • Specify multiple IP addresses for each failover cluster instance. With SQL Server 2005, you can specify multiple IP addresses for each server, allowing you to use all available network IP subnets. SQL Server 2005 limits you to one IP address per network. This provides alternative network connections if one subnet fails.

Failover Clustering Support

In Microsoft SQL Server 2005, the number of nodes supported for failover clustering depends on the operating system. Some operating systems may require fiber optic channels for clustering. For more information, see Hardware and Software Requirements for Installing SQL Server 2005.

For a list of tools, features, and services supported with SQL Server 2005 failover clustering, see Features Supported by the Editions of SQL Server 2005.

See Also


How to: Create a New SQL Server 2005 Failover Cluster (Setup)


Before Installing Failover Clustering

Help and Information

Getting SQL Server 2005 Assistance