The official SQL Server AlwaysOn team blog.
Prepare SQL Server for using AlwaysOn feature
To support AlwaysOn Availability Groups feature, an instance of SQL Server must meet the following prerequisites:
For additional essential information, see Prerequisites, Restrictions, and Recommendations for AlwaysOn Availability Groups (SQL Server) in SQL Server Books Online.
Below are the steps you can follow to enable SQL Server Instance for AlwaysOn Availability Group:
Note: You can perform step1-3 in any order
Go to Administrative Tools, find Failover Cluster Manager.
For more details, see Create a New Failover Cluster
You can also add the node into an existing failover cluster. For information about adding a node into a failover cluster, see Add a Server to a Failover Cluster.
Note: The nodes on which SQL server instance resides on must be in the same failover cluster if the SQL server instances will be in the same availability groups.
After finishing step 1-3, go to SQL Server Configuration Manager to enable the AlwaysOn feature:
SQL Server Configuration Manager saves your change. Then, you must manually restart the SQL Server service. This enables you to choose a restart time that is best for your business requirements. When the SQL Server service restarts, AlwaysOn will be enabled, and the IsHadrEnabled server property will be set to 1.
You can also use the SQL Powershell or WMI provider to enable SQL server for AlwaysOn. For more details, see Enable and Disable AlwaysOn Availability Groups (SQL Server)
Note: After enabling the AlwaysOn feature, if you destroy the failover cluster and create a new failover cluster or add the node to another failover cluster, you MUST disable AlwaysOn and enable it again. The reason is because Enabling AlwaysOn does a lot of other things besides "just flip a registry key", like grant the right permission to SQL server on cluster and cluster registry. So if you destroy the cluster, these permission setting will also be destroyed. You need to disable AlwaysOn to clean up the old local registry key setting and then enable Alwayson again.
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