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Thanks Jeffrey. Does it take more time to recover the databases in alwayson ag or fci failover or is it the same process.
Alwayson and FCI
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Vishu
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Reputation points
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.
SQL Server | Other
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Erland Sommarskog 123K Reputation points MVP Volunteer Moderator2021-07-09T15:47:36.077+00:00 I assume that you with "AlwaysOn" mean "availability groups"? to wit, "Always On" is an umbrella name for the HA features in SQL Server, and covers both availability groups and failover clusters.
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Jeffrey Williams 1,896 Reputation points2021-07-09T16:43:14.337+00:00 In an FCI - you can reduce the amount of time it takes to reallocate the drives from one server to the other using Cluster Shared Volumes.
https://learn.microsoft.com/en-us/windows-server/failover-clustering/failover-cluster-csvs
https://techcommunity.microsoft.com/t5/failover-clustering/cluster-shared-volume-csv-inside-out/ba-p/371872The failover only takes as long as it takes to start SQL Server and recover the databases. It is the recovery of the databases that take the most time.
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Vishu 1,741 Reputation points
2021-07-09T19:02:01.653+00:00 -
Jeffrey Williams 1,896 Reputation points
2021-07-11T15:54:54.267+00:00 SQL Server is already running on the secondary - so a failover only has to work on bringing the databases online during a failover event. That should take less time than starting SQL Server and bringing the databases online - but that may only be a matter of a few seconds. It depends...
For an AG - there is an increased complexity in setting up and managing agent jobs, logins, etc. You have to consider the status of the database(s) on that node - if they are primary then run the job, if they are secondary then skip. Every login has to be created exactly the same on every node (same = same SID and password).
There are advantages/disadvantages to either approach - which should all be considered when determining which methodology to use in your environment.
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Vishu 1,741 Reputation points
2021-07-09T16:11:13.36+00:00 Yes thanks, that is right AlwaysOn refers to Availability group
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Alex Bykovskyi 2,241 Reputation points2021-07-11T07:41:34.43+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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Seeya Xi-MSFT 16,661 Reputation points2021-07-12T10:10:04.017+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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