SQL Server AlwaysOn Availability Group attributes

　　

A primary replica that is used to host the primary database. The primary replica makes a set of primary databases available to read and write connections to clients.

You can configure one or more secondary replicas to support read-only access to the secondary database, and you can configure any secondary replicas to allow backups of the secondary database.

Supports up to eight secondary replicas,

Includes one primary replica and two synchronous-commit secondary replicas (that is, three synchronization nodes) (the secondary replica of the availability group does not need to disconnect the client's existing connection when restoring the transaction log, with the difference between logshipping)

Between 1 primary replicas and another secondary replica can be set to automatic failover (that is, select one of the two synchronous-commit secondary replicas).

One secondary database can hang or fail without affecting other secondary databases, and one primary database can hang or fail without affecting other primary databases.

The deployment of AlwaysOn availability groups requires a WSFC cluster. Each availability replica for a given availability group must be on a different node in the same WSFC.

AlwaysOn availability groups and database mirror actually use the same data synchronization mechanism (including the use of the same endpoint, process, and so on), so these two technologies cannot be deployed in a hybrid way.

SQL Server AlwaysOn Availability Group attributes