SQL Server provides several options for creating high availability for a server or database. The high-availability options include the following:

AlwaysOn Failover Cluster Instances

As part of the SQL Server AlwaysOn offering, AlwaysOn Failover Cluster Instances leverages Windows Server Failover Clustering (WSFC) functionality to provide local high availability through redundancy at the server-instance level—a failover cluster instance (FCI). An FCI is a single instance of SQL Server that is installed across Windows Server Failover Clustering (WSFC) nodes and, possibly, across multiple subnets. On the network, an FCI appears to be an instance of SQL Server running on a single computer, but the FCI provides failover from one WSFC node to another if the current node becomes unavailable.

For more information, see AlwaysOn Failover Cluster Instances (SQL Server).

AlwaysOn Availability Groups

AlwaysOn Availability Groups is an enterprise-level high-availability and disaster recovery solution introduced in SQL Server 2012 to enable you to maximize availability for one or more user databases. AlwaysOn Availability Groups requires that the SQL Server instances reside on Windows Server Failover Clustering (WSFC) nodes. For more information, see AlwaysOn Availability Groups (SQL Server).

Database mirroring

Note
This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature. We recommend that you use AlwaysOn Availability Groups instead.

Database mirroring is a solution to increase database availability by supporting almost instantaneous failover. Database mirroring can be used to maintain a single standby database, ormirror database, for a corresponding production database that is referred to as the principal database. For more information, see Database Mirroring (SQL Server).

Log shipping

Like AlwaysOn Availability Groups and database mirroring, log shipping operates at the database level. You can use log shipping to maintain one or more warm standby databases (referred to as secondary databases) for a single production database that is referred to as the primary database. For more information about log shipping, see About Log Shipping (SQL Server).