AlwaysOn Availability Groups were first introduced with SQL Server 2012, and they are, without a doubt, one of the most compelling reasons to migrate to SQL Server 2012. AlwaysOn Availability Groups enable high availability and disaster recovery for multiple SQL Server databases without the need for a shared storage SAN. Replicas can be used to offload backups and reporting workloads from the primary SQL Server instance.
Related: New Features in SQL Server 2014
AlwaysOn Availability Groups provide high availability for multiple databases, and they can make use of multiple secondary replicas. Each secondary SQL Server replica has its own copy of the protected databases. AlwaysOn Availability Groups continuously synchronize transactions from the primary replica to each of the secondary replicas. This replication can be configured as synchronous or asynchronous to support local high availability or remote disaster recovery.
In addition, here are some major enhancements to AlwaysOn Availability Groups in SQL Server 2014 that you might want to be aware of:
Enhanced Availability for Read-Only Replicas
One of the advantages of AlwaysOn Availability Groups is that the secondary replicas can be used for reporting and backup. With SQL Server 2014, the availability of secondary replicas has been enhanced to allow read workloads to continue to run even in the case of lengthy network failures or the loss of quorum for the Windows Server Failover Cluster.
Increased Number of Replicas
Another important enhancement in SQL Server 2014 is the increased maximum number of secondaries. SQL Server 2012 supported a maximum of four secondary replicas. With SQL Server 2014, AlwaysOn Availability Groups now supports up to eight secondary replicas. The additional secondary replicas can be used to distribute read workloads and provide enhanced recoverability.
Integration with Windows Azure
SQL Server 2014 AlwaysOn Availability Groups use Windows Azure in a couple of different ways. On-premises SQL Server instances can use the new Windows Azure configuration options in the AlwaysOn Availability Group wizard to create one or more asynchronous secondary replicas on Windows Azure Infrastructure as a Service (IaaS) services. This enables you to manually fail over to a SQL Server instance running on Windows Azure. As with a typical secondary replica, Windows Azure replicas can be used to offload reporting workloads and to perform backups.
In addition, you can also use SQL Server 2014 AlwaysOn Availability Groups to provide high availability for SQL Server databases hosted in Windows Azure. SQL Server 2014 instances running on Windows Azure IaaS Services can configure a synchronous secondary replica in Azure for automatic failover in case of server or VM failure.
Enhanced Diagnostics
SQL Server 2014 AlwaysOn Availability Groups diagnostic and troubleshooting message display has been improved to offer more specific information. Additional columns have also been made more discoverable in the AlwaysOn Dashboard.
You can learn more about the enhancements to AlwaysOne Availability Groups and other SQL Server 2014 features at the Microsoft SQL Server 2014 website. You can also download the SQL Server 2014 CTP1 from TechNet.
