Microsoft® Windows NT® Clustering Service is a feature of Windows NT Server Enterprise Edition, which supports the connection of two servers, or nodes, into a cluster for manageability of data and applications. Clustering Service monitors both servers, and detects and recovers from server or application failures automatically.
SQL Server Failover Support is available only with the Enterprise Edition of SQL Server version 7.0 and is designed to work in conjunction with Clustering Service. Failover Support provides the ability to make SQL Server appear as a single SQL Server virtual server when installed on a cluster. Client connections see only the single SQL Server virtual server and are unaware which physical Windows NT Server node is processing their request. As a virtual server, SQL Server is managed through Cluster Administrator from either node of the cluster.
Clustering Service monitors the status of the primary and secondary nodes, the SQL Server application, and shared disk resources. Upon failure of the primary node, services will fail over automatically to the secondary node, rolling back uncommitted transactions in preparation for client reconnection to the database. Applications designed to work with Clustering Service can make the recovery of data and applications appear seamless to clients.