Microsoft® SQL Server 2012 Unleashed

AlwaysOn Availability Groups

Figure 43.1 also shows the availability group capability. Availability groups are focused on database-level failover and availability by utilizing a data redundancy approach. Again, borrowing from the database mirroring experience (and underlying technologies), a transactionally consistent secondary replica is made that can be used for both read-only access (active for use at all times) and for failover if the primary database (primary replica) fails for any reason. In Figure 43.1, you can see a SQL Server AlwaysOn availability group being used 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 an