The data for a large Web site or internal online transaction processing (OLTP) system must be highly reliable. The data must be available 24 hours a day, 7 days a week, 52 weeks a year. In a clustered application tier, the loss of one server may degrade system performance, but it will not stop the entire system. The remaining servers in the cluster rebalance the load until a replacement server can be plugged into the cluster.
Although Microsoft® SQL Server™ 2000 does not support this type of load-balanced clustering, it does support Microsoft Cluster Services failover clustering. Failover clustering supports one to four servers per cluster depending on the operating system. The cluster appears to applications as a single virtual server. If the primary server node fails, another node detects the loss of the primary and automatically starts servicing all requests sent to the virtual server. The cluster remains running under the alternative node until the primary server is repaired or replaced. Failover clustering helps provide high availability, but it does not perform any load balancing.