SQL Server Failover Cluster Instances
SQL Server Failover Cluster Instances (FCI) is a high-availability solution that provides redundancy at the server-instance level by running a single instance of SQL Server across multiple Windows Server Failover Clustering (WSFC) nodes. It ensures minimal downtime during hardware or software failures by automatically failing over the SQL Server instance to another node in the cluster, maintaining service continuity. This solution is built on shared storage, such as a SAN or SMB file share, which all cluster nodes can access.
Developers and database administrators should use SQL Server FCI when they need to ensure high availability for mission-critical applications with minimal downtime, such as in financial systems, healthcare databases, or e-commerce platforms. It is particularly suitable for scenarios where automatic failover is required without data loss, and when using shared storage is feasible, as it provides a robust solution for hardware failures, OS crashes, or planned maintenance. However, it does not protect against storage-level failures, so it should be combined with other technologies like Always On Availability Groups for comprehensive disaster recovery.