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Understanding Quorum majority in a Failover Cluster RRS feed

  • Question

  • Hi

    We have a windows cluster with 3 nodes and no witness on windows 2016
    Quorum type : NODE_MAJORITY
    Number of Quorum Votes : 1 for each node

    I am simulating a DR by shutting down Node 2 and Node 3, since every node has 1 vote and we are using node majority config, I am expecting that the cluster will fail and I have to start the cluster with "forcequorum" option to establish a service and bring Always ON and SQL online

    This was not the case, the cluster is still up and Always ON running on Node 1 even if Node 2 and 3 are down and we lost node majority,  I am also able to reproduce the case using microsoft handsonlabs (Config Always ON availability group)
    https://www.microsoft.com/handsonlabs/selfpacedlabs

    Any explanation on this behavior?

    Best regards


    • Edited by S Rym Friday, September 20, 2019 3:08 PM
    Friday, September 20, 2019 3:08 PM

Answers

  • Like others have said its Dynamic quorum playing its role. With Windows server 2012 R2 there were two major concepts 

    1. Dynamic quorum

    2 Dynamic Witness

    They work had in hand. With above 2 your WSFC can remain online even if all the nodes(but one) are "gracefully" this is what you are seeing. The last node remaining is still online as cluster adjusted its quorum and removed the voting power of the nodes which went down. So for cluster there is only one node and it has a quorum. BUT point to note here is IF both the nodes go down abruptly, like in case of DC failure or RACK failure, the WSFC dynamic quorum and witness would not be able to work try it.


    Cheers,

    Shashank

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    • Marked as answer by S Rym Monday, September 23, 2019 4:05 PM
    Monday, September 23, 2019 6:52 AM
    Moderator

All replies

  • It could be Dynamic quorum (available with Windows Server 2012) where even though the number of nodes are less than a majority, the cluster continues to run due to the nodes being shut down sequentially. Explained here - Dynamic Quorum
    Friday, September 20, 2019 3:27 PM
  • Hi S Rym,

    According to your description, it should be dynamic quorum. Dynamic quorum will dynamically adjust dynamic weight of the node when you start losing nodes. For more information, please refer to this blog.

    >>I am expecting that the cluster will fail and I have to start the cluster with "forcequorum" option to establish a service and bring Always ON and SQL online

    If you want  the cluster to  fail and start the cluster with force quorum option, you can disable the Dynamic Quorum by running this command(execute on one of the cluster nodes):

    (Get-Cluster).DynamicQuorum = 0

    Help those could help you.

    Best Regards,

    Amelia Gu


    MSDN Community Support
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    Monday, September 23, 2019 5:43 AM
  • Like others have said its Dynamic quorum playing its role. With Windows server 2012 R2 there were two major concepts 

    1. Dynamic quorum

    2 Dynamic Witness

    They work had in hand. With above 2 your WSFC can remain online even if all the nodes(but one) are "gracefully" this is what you are seeing. The last node remaining is still online as cluster adjusted its quorum and removed the voting power of the nodes which went down. So for cluster there is only one node and it has a quorum. BUT point to note here is IF both the nodes go down abruptly, like in case of DC failure or RACK failure, the WSFC dynamic quorum and witness would not be able to work try it.


    Cheers,

    Shashank

    Please mark this reply as answer if it solved your issue or vote as helpful if it helped so that other forum members can benefit from it

    My TechNet Wiki Articles

    MVP

    • Marked as answer by S Rym Monday, September 23, 2019 4:05 PM
    Monday, September 23, 2019 6:52 AM
    Moderator
  • Hi,

    Thanks all for you replay, yes the custer was in Dynamic mode and after disabling the dynamic quorum mode temporary for our DR tests everything is behaving as expeted, thx again for the info and for the links

    Best regards

    Monday, September 23, 2019 4:10 PM