Blog Post

Alwayson Availability Groups vs Alwayson Failover Cluster Instances


SQL Server is one of the finest database management system deployed by organizations for storing and retrieving their data. It facilitates the function of data storing and retrieving by the applications which either run on the same or different platforms. The dominant reason behind the deployment of SQL Server on a large scale is the huge list of features that it offers. One such feature is AlwaysOn offering. In this blog, we will put forth discussion on AlwaysOn Availability Group & AlwaysOn Failover Instance.

AlwaysOn Availability Group

The AlwaysOn Availability Groups is a disaster recovery solution is used for providing alternative solution to database mirroring at the enterprise-level. It maximizes the availability of the databases belonging to an enterprise. It supports two databases-Primary and Secondary. While the primary database is a set of read and write primary databases, the secondary databases are the corresponding databases of one to eight sets associated with primary database.

Benefits of Alwayson Availability Groups:

The list of benefits offered by Always On Availability Group goes as follows:

  • It extends support to provide nine availability replicas. Since availability replica is used to maintain a local copy of all the databases, they prove to be very crucial in ensuring database availability at the time of data disasters.
  • It offers two availability modes-Asynchronous and Synchronous commit mode.
  • It supports variant failovers like planned manual failover, automatic failover and forced failover.
  • Enables users to configure availability replica for supporting one or both the active-secondary capabilities, as per the user’s requirement.

AlwaysOn Failover Cluster Instance

SQL Server AlwaysOn Failover Cluster Instance or FCI, a substantial offering of AlwaysOn, provides high availability at the server-instance level by making use of Windows Server Failover Clustering. It is a single instance of SQL, which is installed across Windows Server Failover Cluster nodes. In a network, FCI seems to be an instance, which runs on a single computer. However, in real it provides failover to the other node in the scenario if one WSFC node is unavailable.

In the instance of any hardware or software failure of the SQL Server, the clients and the applications connected to it, experience downtime. The high availability of the instances of SQL Server is safeguarded by the redundant node, whenever the instances are configured to be a Failover Cluster Instance.

Benefits of AlwaysOn Failover Cluster Instance:

  • The feature of redundancy provides protection of the SQL Server instances.
  • Occurrence of automatic failover whenever any failure like OS failure, hardware failure or application failure occurs.
  • Provides a support to a broad range of WSFC cluster disks, storage solutions, etc.
  • It does not require reconfiguration of the clients and applications associated with the Server instances during failovers.


AlwaysOn Availability Group and AlwaysOn Failover Instance are the two provisions that enable the users to increase the availability of SQL Server instance. Both the provisions have their associated advantages and limitations and thus the organizations should make use of either of them according to their requirement.


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