Always On in SQL Server 2017 (Read-Scale Feature)

Always On in SQL Server 2017 (Read-Scale Feature)

SQL server 2017 has introduced new feature and technology (read-scale availability group) with Always on. Now, Always On availability groups provide high availability, disaster recovery and read-scale balancing.

Read-Scale Availability Group: This architecture provides replicas for read-only workloads but no HA. There is a question why we need this new architecture:

In SQL Server 2016 and before, all availability groups required a cluster and cluster provides a business continuity HADR. SQL Server 2017 introduces read-scale availability groups without a cluster.

This feature is very useful in case if the business needs to keep the resources for mission-critical workloads running on the primary then users can route to readable secondary replicas without using any cluster technology.

CLUSTER_TYPE:  There are three different cluster types which are used while creating availability group as below

  • WSFCWinows server failover cluster. On Windows, it is the default value for CLUSTER_TYPE.
  • EXTERNALA cluster manager that is not Windows server failover cluster – for example, on Linux with Pacemaker.
  • NONENo cluster manager. Used for a read-scale availability group.

How to get the details for cluster type used in availability group:

DMV:  sys.availability_groups

Two new columns:  cluster_type and cluster_type_desc


Select name as ‘Availability Groups ’, cluster_type, cluster_type_desc from sys.availability_groups.

Thanks for reading!

Awaiting your valuable responses…




About Mirza Husain

Mirza Husain is a senior consultant-database and having more than 10+ years of experience in the IT industry with different domains. He is fond of writing and speaking about SQL Server and also keen to learn new technologies. He is holding MCA degree and having Microsoft certifications as MCP & MCTS. He is also ITIL certified. In his past years, he worked with many clients as Microsoft, Bank of America etc. Currently he is associated with a France based client and offering his best services. You may reach him on his email id -- Thanks!
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