AlwaysOn Availability Groups SQL Server

AlwaysOn Availability Groups SQL Server

In this post we will learn about AlwaysOn Availability Groups SQL Server. AlwaysOn Availability Groups was first introduced in SQL Server 2012. AlwaysOn Availability Groups SQL Server is the successor of Database mirroring which was introduced with SQL Server 2005 SP1, Database mirroring is a great feature for High Availability and Disaster Recovery, but Database Mirroring had some limitations which does not make it that much familiar.

Database Mirroring Limitations:

1. You can only mirror 1 database through a Database Mirroring.

2. The Failover is done on the Mirroring session level, which means you can only failover 1 database at a given time.

3. Only 1 Mirroring partner possible.

4. Mirroring database is not available for read-only access.

AlwaysOn Availability Groups offers you the following advantages over traditional Database Mirroring:

1. Multi-Database Failovers
2. Multiple Secondaries
3. Active Secondaries
4. Integrated HA Management

AlwaysOn Availability Groups in SQL Server provide high availability for multiple databases, and make multiple secondary replicas. Every secondary SQL Server replica has its own copy of the protected databases. AlwaysOn Availability Groups continuously synchronize transactions from the primary replica server to each of the secondary replicas server. This replication can be configured as synchronous or asynchronous to support local high availability or remote disaster recovery.

AlwaysOn Availability Group is created between several standalone SQL Server instances. Minimum 2 different SQL Server instances is required for AlwaysOn Availability Group. All instances that participating in an AlwaysOn Availability Group don’t need any Shared Storage – each SQL Server instance has its own local storage. But each participating SQL Server instance must be in the same Windows Domain