Microsoft has made great improvements in the area of High Availability since Database Mirroring was introduced with the release of SQL Server 2005. Many of the limitations of this feature have been addressed with the release of AlwaysOn Availability Groups as part of SQL Server 2012, and subsequently enhanced in SQL Server 2014. Outlined below are the benefits and limitations of these two technologies:
Database Mirroring:
SQL Server 2012 & 2014 provides AlwaysOn Availability Groups which seeks to address these limitations. SQL Server AlwaysOn Availability Groups key features include:
This diagram shows an implementation of availability group that contains themaximum possible number of availability replicas on SQL Server 2012. In SQL Server 2014 you could add a further four secondary replicas. Initially the primary node AVG can be created and HA (High Availability) or DR (Disaster Recovery) nodes could be added when required.
Database Mirroring is still available in SQL2012 and SQL2014, but will be deprecated in future SQL Server releases.
Detailed SQL Server AlwaysOn information can be found on theMicrosoft site, or by contacting andersenIT.