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What is AlwaysOn in SQL Server?

Posted by Jean Paul on March 3, 2014

SQL Server 2012 introduced the new feature called AlwaysOn.

AlwaysOn provides High Availability & Disaster Recovery alternative to Database Mirroring.

What is Database Mirroring?

Database Mirroring is a technique to increase High Availability of database.  The topology consists of three server roles.

  1. Witness Server
  2. Principal Server
  3. Mirror Server 

Transaction Logs will be synchronized from Principal Server to Mirror Server.


The Witness Server determines whether to contact Principal or Mirror based on activity, thus increasing the availability.

Advantages of AlwaysOn over Database Mirroring

AlwaysOn provides the following advantages over Database Mirroring:

  1. More effective server utilization
  2. Less configuration hassles
  3. Better manageability
  4. Better failover situation
  5. Works best with multiple-database scenarios of SharePoint

More and More people are switching to AlwaysOn Availability Group technique.


AlwaysOn Experiment


Clustering, Mirroring, Log Shipping, AlwaysOn are different technologies to attain High Availability in database servers.

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