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  • Question

  • What quorum mode is recommended if there’re even numbers of nodes in a cluster?


    Md. shams

    Wednesday, January 8, 2014 11:04 AM

All replies

  • Node & Disk Majority

    This quorum configuration is most commonly used since it works well with 2-node and 4-node clusters which are the most common deployments.  This configuration is used when there is an even number of nodes in the cluster.  In this configuration, every node gets 1 vote, and additionally 1 disk gets 1 vote, so there is generally an odd number of total votes. 

    This disk is called the Disk Witness (sometimes referred to as the ‘quorum disk’) and is simply a small clustered disk which is in the Cluster Available Storage group.  This disk is highly-available and can failover between nodes.  It is considered part of the Cluster Core Resources group, however it is generally hidden from view in Failover Cluster Manager since it does not need to be interacted with.

    Since there are an even number of nodes and 1 addition Disk Witness vote, in total there will be an odd number of votes.  If there is a partition between two subsets of nodes, the subset with more than half the votes will maintain quorum.  For example, if a 4-node cluster with a Disk Witness partitions into a 2-node subset and another 2-node subset, one of those subsets will also own the Disk Witness, so it will have 3 total votes and will stay online.  The 2-node subset will offline until it can reconnect with the other 3 voters.  This means that the cluster can lose communication with any two voters, whether they are 2 nodes, or 1 node and the Witness Disk.

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    • Proposed as answer by AV111 Tuesday, May 5, 2015 2:51 PM
    • Edited by AV111 Tuesday, May 5, 2015 3:38 PM
    • Unproposed as answer by AV111 Friday, May 8, 2015 2:37 PM
    Tuesday, May 5, 2015 2:51 PM