SQL Server 2012 Availability Groups Lessons Pt 5
This is the fifth tip on SQL Server 2012 availability groups to make sure you get your design right.
Tip 5: You are limited in SQL Server 2012 availability groups to having a maximum of two synchronous secondaries. This may seem more than enough, but when you need up to date data in all your AG databases then you may have a problem. We needed three synchronous secondaries, one for same site high availability with automatic failover, another for same site reporting and the third as the DR site high availability with manual failover. This configuration is not achievable in SQL Server 2012. You will have to look at other solutions, potentially one involving the synchronisation of your DR site through other technologies (e.g. transactional replication).
Extra Tip: Don't try to use the "old" (SQL 2008) mirroring on the same database as a workaround. The database mirroring endpoints are already being used by HADR.
NB: With SQL Server 2014 and 2016 the number and configuration of secondaries has now changed. Please refer to product features for these more recent releases.