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Yehoram Dan

Yehoram Dan

Professional SQL server DBA with over 20 years of experience with enterprise organizations. Yehoram is responsible for consulting and providing advanced solutions to Experda's customers.

Always On Technology 2016

Making Basic Availability Groups (Always On Availability Groups)

React as Advanced Availability Groups (Always On Availability Groups)

Always On Basic Availability Groups provide a basic availability solution for SQL Server 2016 and SQL Server 2017 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.

Features

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.

Limitations

  • 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 the secondary replica.
  • No backups on the 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.
  • 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.

Configuration

An Always-On basic availability group can be created on any two SQL Server 2016 Standard Edition servers. When you create a basic availability group, you must specify both replicas during creation.

To create a basic availability group, use the CREATE AVAILABILITY GROUP Transact-SQL command and specify the WITH BASIC option (the default is ADVANCED). You can also create the basic availability group using the UI in SQL Server Management Studio starting with version 17.8. For more information, see CREATE AVAILABILITY GROUP (Transact-SQL).

Making Standard Edition react as Advanced edition:

By Providing an Extension JOBS We could achieve an advanced availability group features to the basic availability group as following:

A Basic option is configured only one Database to an Availability group.

We will configure a job that will perform failover of all declared groups.

Basic Availability group’s limitation is only one Primary replica and on the secondary replica

By using the same job and script we can achieve a replica chaining Thus: more than one secondary.

By using the same Attitude We also can achieve

  • Backups on a secondary replica
  • Integrity checks on secondary replicas

Which we miss in a standard edition.

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