Shulou(Shulou.com)06/01 Report--

two。 AlwaysOn availability groups created for high availability

In the AlwaysOn availability group of the Linux platform, the SQL Server instance stores configuration metadata in the master database. Configure CLUSTER_TYPE = EXTERNAL in the AlwaysOn availability group on the Linux cluster. At this point, there is no WSFC to arbitrate the failover. In this case, the configuration metadata is managed and maintained by the SQL Server instance. Because there is no witness in the cluster, a third SQL Server instance is required to store configuration status metadata. All three SQL Server instances work together to provide distributed metadata storage for the cluster.

Cluster Administrator can query SQL Server instances in availability groups and coordinate failover to maintain high availability. In a Linux cluster, Pacemaker is the cluster administrator.

SQL Server 2017 CU1 enables high availability for two synchronous replicas plus an availability group with only configured replicas, configured as CLUSTER_TYPE = EXTERNAL. This only copy of the configuration can be located in any version of SQL Server 2017 CU1 or later, including the SQL Server Express version. Only the configuration copy maintains configuration information about the availability group in the master database, but does not contain the user database for the availability group.

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