Standard Edition only allows Always On setup in basic mode. Switch to Enterprise Edition for full Always On features.
Always On Basic Mode (Standard Edition) Limitations
Basic availability groups use a subset of features compared to advanced availability groups on SQL Server Enterprise Edition. Basic availability groups include the following limitations:
- Limit of two replicas (primary and secondary). Basic Availability Groups for SQL Server 2017 on Linux support an additional configuration only replica.
- No read access on secondary replica.
- No backups on secondary replica.
- No integrity checks on secondary replicas.
- No support for replicas hosted on servers running a version of SQL Server prior to SQL Server 2016 Community Technology Preview 3 (CTP3).
- Support for one availability database. For multiple databases, you have to setup multiple AG groups.
- 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 servers.
- Basic availability groups cannot be part of a distributed availability group.
- You may have multiple Basic availability groups connected to a single instance of SQL Server.