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A SQL Server Always On Failover Cluster Instance (FCI) relies on Windows Server Failover Clustering (WSFC) or on Pacemaker when running FCI on Linux. FCI is the basis of many enterprise SQL Server deployments. FCI operates at the SQL Server instance level to protect all databases and resources within a SQL Server instance. A basic SQL Server FCI runs on two or more servers and requires shared storage between them. If an issue is detected on the SQL Server instance, that SQL instance will be restarted on another server in the cluster, and the restarted instance will bring related databases online. WSFC provides the ability to configure cluster service dependencies and preferences, so that required services and resources appear online in the correct order and on the correct cluster nodes. SQL Server FCI features can be used to complement or provide options for other HA solutions. For complete information, see the Microsoft Always On Failover Cluster Instances page.