9.3. Failover Clustering
Failover clustering is used to provide redundancy at the server level. In other words, if you want to ensure that services remain running on a server even if the server fails, you can implement failover clustering. Failover clustering is often used in situations where you can't afford any outage for a particular service or you need to ensure the service is highly available.
In previous versions of Windows, failover clusters were known as server clusters. In Windows Server 2008, the terminology is failover clusters or failover clustering.
Some of the common uses of failover clusters include the following:
Database servers (such as Microsoft SQL Server)
Email servers (such as Microsoft Exchange)