AlwaysOn (Codename. Hadron ((High Availability Disaster Recovery Always On)) was introduced in SQL Server 2012. It’s one of the most powerful high availability technology introduced in SQL Server and is one of the compelling reasons to migrate to SQL Server 2012 that provides reliable, integrated, flexible and efficient high availability and disaster recovery solution. In brief, AlwaysOn availability groups enable HADR for multiple databases with the need of expensive SAN hardware and you can offload many tasks/operations like (Queries, Reporting, Backups, Maintenance, etc.) to the secondary replicas and Primary replica can be used for write purpose. Data is copied per log record from Primary to secondary servers either synchronously or asynchronously.