Microsoft® SQL Server 2012 Unleashed

AlwaysOn Availability Groups

Also new in SQL Server 2012 is the Availability Group capability. This is focused on database-level failover and availability by utilizing a data redundancy approach. Again, borrowing on the database mirroring experience (and underlying technologies), a transactionally consistent secondary replica is made that can be used for both read-only access (it is active for use at all times) as well as for failover if the primary database (primary replica) fails for any reason. In Figure 39.8, you can see a SQL Server AlwaysOn Availability Group being utilized for HA and even for distributing the read-only workload off of the primary SQL Server instance to the secondary replica. You can have up to four secondary replicas in ...