Configure Windows Failover Cluster for Always On Availability Groupįirst of all, we must configure a failover cluster on all nodes used by Always On. The Listener is also responsible for balancing SELECT queries between secondary replicas. Since users connect to the Listener (a special cluster IP address and the corresponding DNS name) when working with Always On, it will become possible to run write queries again. If a primary replica fails, the cluster will vote for a new primary replica, and Always On will make one of the secondary replicas a primary one. Each availability group may have up to 8 secondary replicas. Each SQL Server instance can have multiple availability groups. Each availability group node must be a member of a Windows failover cluster. Each replica may contain one or more databases.Īlways On is based on WSFC. Replica is an SQL Server instance in the availability group.Always On Availability Group is a set of replicas and databases.You can read about MS SQL Server licensing aspects here. There are no restrictions in the Enterprise edition. Only 1 database per availability group is supported.The secondary replica cannot be used to backup MS SQL.The secondary replica cannot be used to read data.
It is limited to 2 replicas (primary and secondary).When building a Linux-based cluster, you can use Pacemaker instead of WSFC.Īlways On is available in the Standard edition, but it has some restrictions: Starting from MS SQL Server 2017, Always On may be used without WSFC and in Linux hosts as well. WSFC monitors availability group nodes and provides automatic failover.
Each replica keeps copies of the availability group database.Īlways On is based on Windows Server Failover Cluster (WSFC). Load balancing of SELECT queries between nodes (secondary replicas may be readable).MS SQL high availability and automatic failover.What can you use SQL Server availability groups for? SQL Server Always On: Operability Check & Failoverįeatures of Always On Availability Groups in SQL Server.Configuring Always On Availability Group on MS SQL Server.Configure Windows Failover Cluster for Always On Availability Group.