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understand dynamic quorum RRS feed

  • Question

  • Please explain the below statement & in which context they are using it. 

    Can survive one server failure, then another: Yes

    https://docs.microsoft.com/en-us/windows-server/storage/storage-spaces/understand-quorum

    Wednesday, April 10, 2019 7:09 PM

All replies

  • Hi Rana,

    If we take the following example from the documentation you linked:


    This is a two-node cluster with a witness, meaning there are a total of 3 votes.

    This means that the cluster can survive one (1) failure:

    • Can survive one server failure: Yes.


    So what it means is that the cluster can survive if one (1) server node either Node 1 OR Node 2 goes down.


    If Node 1 goes down, the cluster will still be online and functional with Node 2 + Witness, because the majority is determined which means the cluster still has 2/3 votes.


    If Node 2 goes down, the cluster will still be online and functional with Node 1 + Witness, because the majority is determined which means the cluster still has 2/3 votes.


    Best regards,
    Leon


    Blog: https://thesystemcenterblog.com LinkedIn:

    Wednesday, April 10, 2019 8:43 PM
  • https://blogs.technet.microsoft.com/askcore/2016/03/21/behavior-of-dynamic-witness-on-windows-server-2012-r2-failover-clustering-3/ is a blog post by the cluster engineering team to provide an explanation of how dynamic quorum works.

    tim

    Thursday, April 11, 2019 12:36 PM
  • Hi,

    i assume that you are very clear with the quorum. It is the majority number of votes available to keep the cluster and its services running.

    In an 8 node cluster, the majority is 5 (4+1). So it can sustain upto 3 nodes failure. So it is said to have a witness (disk or fileshare) to have a vote and participate. This will give us a little more advantage of going upto 4 nodes failure at a time. So having said this, lets see what dynamic quorum is

    The dynamic quorum is introduced in windows 2012 onwards. This concept will further help us to afford more nodes failure without interrupting the clustered application. In the same 8 node cluster, if a node fails, then the quorum is considered for the currently available number nodes. And still one more node goes down, now the quorum (majority) is calculated for the currently available nodes only. i.e. the votes of the failed nodes are ignored for the quorum calculation. It can also be said that, when 2 nodes are failed in an 8 nodes cluster, then the cluster behaves like a 6 nodes cluster only (ignoring the failed nodes' vote). Thus dynamic quorum can go upto one node being available in the cluster, provided that the single node can handle the clustered workload. This works well when there was a gradual failure of the nodes in the cluster. If there is a sudden failure of half or more number of the nodes, then the cluster more likely fails.

    In windows 2012 R2 onwards, there is a concept called dynamic witness. This gives more advantage that, the cluster will decide whether to consider the vote of the witness (or not) during failure. It is said that even number of nodes cluster is recommended to have a witness, so as to gain an advantage of affording one more node failure than without witness. So if we have a witness added to the cluster, the cluster will consider the witness's vote when the number of available nodes is even number and will not consider when the available number of nodes is odd number. This is to reduce the impact of the worst case scenario in which the cluster will fail when there was a sudden failure of half number of nodes in the cluster

    So this is what is said, that the cluster can survive one node failure and then another which means the nodes going down gradually one by one.

    hope this helps you to understand!!

    Regards.
    Bala N

    Thursday, April 11, 2019 1:50 PM
  • Hi,

    Dynamic Quorum is the ability of a Windows Server failover cluster to recalculate quorum when nodes fail or shut down sequentially.

    In a failover cluster, quorum is the number of elements that must be online for that cluster to continue running. As a new feature in Windows Server 2012, Dynamic Quorum works on two conditions: the first condition is that the cluster has already achieved quorum; the second condition is that sequential nodes have failed. When nodes shut down sequentially, Dynamic Quorum allows the cluster to continue running with less than a majority of active nodes.

    Dynamic Quorum is automatically used by Failover Clustering to rig the vote in case there is a chance of a tied vote, where a vote will be stripped from one of the nodes.

    Here’s an article talked about Dynamic Quorum in detail, hope it can help.

    https://www.petri.com/what-is-windows-server-2012-r2-dynamic-quorum

    Highly appreciate your effort and time. If you have any question or concern, please feel free to let me know.

    Best regards,

    Michael


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    Friday, April 12, 2019 8:00 AM
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  • Hi,

    Just want to confirm the current situation.

    Please feel free to let us know if you need further assistance.

    Best regards,

    Michael


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    Sunday, April 14, 2019 7:11 AM
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  • Hi,

    Could the above reply be of help? If yes, you may mark it as answer, if not, feel free to feed back.

    Best Regards,

    Michael


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    Monday, April 15, 2019 9:51 AM
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  • Hi,

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    Michael


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    Wednesday, April 17, 2019 2:25 AM
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