Alwayson and FCI

Vishu 1,556 Reputation points
2021-07-09T12:57:13.403+00:00

Experts,

Understanding is that a FCI would take more time to failover vs AlwaysOn because of the SQL Instance restarting and the realignment of disks on the Secondary Node but if the realignment of disks and Instance restart on the other node happens in say 30 seconds, can we say that difference between the failover of the two(FCI and AwlaysOn) with along recovery of all databases is approx 30 seconds.

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  1. Vishu 1,556 Reputation points
    2021-07-09T19:02:01.653+00:00

    Thanks Jeffrey. Does it take more time to recover the databases in alwayson ag or fci failover or is it the same process.

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  1. Vishu 1,556 Reputation points
    2021-07-09T16:11:13.36+00:00

    Yes thanks, that is right AlwaysOn refers to Availability group

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  2. Alex Bykovskyi 1,836 Reputation points
    2021-07-11T07:41:34.43+00:00

    Hey,

    Always On Availability Groups should failover quicker than FCI. It is due to architecture. In synchronous commit mode you have at least to replicas running (primary and secondary), and failover occurs within seconds. https://www.sqlshack.com/explore-failover-types-in-sql-server-always-on-availability-groups/

    In FCI in case of failover the role will start on another server, which will take more time. In addition, SQL FCI requires shared storage such as SAN or any kind of SDS. StarWind VSAN can be used as a shared storage option. Might help:
    https://www.starwindsoftware.com/resource-library/starwind-virtual-san-installing-and-configuring-sql-server-2019-tp-failover-cluster-instance-on-windows-server-2016/

    Cheers,

    Alex Bykovskyi

    StarWind Software

    Note: Posts are provided “AS IS” without warranty of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose.

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  3. Seeya Xi-MSFT 16,456 Reputation points
    2021-07-12T10:10:04.017+00:00

    Hi @Vishu ,

    As for the differences between FCI and AG, please refer to this: Comparison of Failover Cluster Instances and Availability Groups.
    For the Comparison,
    https://www.sqlservercentral.com/forums/topic/fci-vs-always-on-ag
    https://dba.stackexchange.com/questions/196793/alwayson-ag-versus-fci
    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.

    Best regards,
    Seeya


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