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There are several quorum types: Node Majority,Node and Disk Majority,Node and File Share Majority,No Majority: Disk Only

I did not modify any quorum settings when setting up a Server 2012 R2 cluster and I can see it chose "Node Majority" as the quorum type:

Cluster        : VDI-CS-01
QuorumResource :
QuorumType     : NodeMajority

This is a simple 2 node cluster- I have not added a witness yet.

But because this a 2012 cluster and dynamic quorum is enable automatically, does the quorum type even matter? If there is a series of node failures won't it automatically move the quorum to available nodes until there is only one left?

I'm confused as to how dynamic quorum relates to the quorum type set on a Windows cluster.

HopelessN00b
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red888
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1 Answers1

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Dynamic quorum doesn't work by changing the quorum type, it works by modifying the NodeWeight property on one or more nodes as required.

For example, let's say I have a three node cluster running in Node Majority quorum mode. You would choose this mode as it gives the quorum an odd number of participating votes, which is required in order to make a decision.

Now let's say I lose a node. With a traditional quorum configuration, I am now running in Node Majority mode but with two votes. This means that if I lose another node without changing any of the quorum settings (either modifying the type or the NodeWeight of one of the nodes), my cluster will go down if I lose a second node.

With a dynamic quorum, the cluster will recalculate the NodeWeights on the fly. It sees that I have an even number of nodes, so it sets the NodeWeight of one of my remaining nodes to zero. Thus, that node does not effectively have a vote in the quroum, and I'm back to an odd vote count. Now if another node fails, my cluster will stay up on the remaining nodes.

You still need to select the appropriate quorum type for your configuration, dynamic quroum just works within that type to set NodeWeights as necessary to maintain cluster uptime. You still decide from the beginning if you are going to use, for example, a file share witness or a witness disk as a quorum participant. Dynamic quroum will only work if the failures have been sequential rather than simultaneous, meaning the cluster has had time to recover and recalculate between events.

phoebus
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  • Very concise, thanks. So if 2 nodes in a 3 Node Majority cluster failed simultaneously I would be able to manually adjust the weight of the remaining node and bring it back up with the other 2 still down? – red888 Nov 14 '13 at 15:36
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    Hm, to be honest I haven't tried a post-failure adjustment. Typically a manual adjustment of NodeWeight would be done to allow you, for example, to use a file share witness in a cluster with an odd number of nodes. I will see if I have time to try this out in a lab environment. – phoebus Nov 14 '13 at 15:40