Basic Availability Groups (Always On Availability Groups)
Always On Basic Availability Groups provide a high availability solution for SQL Server 2016 Standard Edition. A basic availability group supports a failover environment for a single database. It is created and managed much like traditional (advanced) Always On Availability Groups (SQL Server) with Enterprise Edition. The differences and limitations of basic availability groups are summarized in this document.
Always On Basic Availability Groups replaces the deprecated Database Mirroring feature and provides a similar level of feature support. Basic availability groups enable a primary database to maintain a single replica. This replica can use either synchronous-commit mode or asynchronous-commit mode. For more information about availability modes, see Availability Modes (Always On Availability Groups). The secondary replica remains inactive unless there is a need to failover. This failover reverses the primary and secondary role assignments, causing the secondary replica to become the primary active database. For more information on failover, see Failover and Failover Modes (Always On Availability Groups). Basic availability groups can operate in a hybrid environment that spans on-premises and Microsoft Azure.
Basic availability groups use a subset of features compared to advanced availability groups on SQL Server 2016 Enterprise Edition. Basic availability groups include the following limitations:
Limit of two replicas (primary and secondary).
No read access on secondary replica.
No backups on secondary replica.
No support for replicas hosted on servers running a version of SQL Server prior to SQL Server 2016 Community Technology Preview 3 (CTP3).
No support for adding or removing a replica to an existing basic availability group.
Support for one availability database.
Basic availability groups cannot be upgraded to advanced availability groups. The group must be dropped and re-added to a group that contains servers running only SQL Server 2016 Enterprise Edition.
Basic availability groups are only supported for Standard Edition server