Q: What is Dynamic Witness in Windows Server 2012 R2 Failover Clustering?

A: Prior to Windows Server 2012 R2, the guidance was to configure a witness if there was an even number of nodes, because its important to have an odd total number of votes in circumstances where the cluster becomes partitioned.

The problem is that if a node fails within a cluster with an odd number of nodes, that leaves the cluster with an even number of votes, which is potentially a problem. At this point you might then want to add a witness.

However, Windows Server 2012 R2 fixes this by changing the guidance to always configure a witness, either a disk witness or file-share witness. The clustering service will automatically assign the witness a vote, the witness dynamic vote, depending on if there is an odd or even number of votes present for the cluster nodes.

  • If there are an even number of nodes that have a vote (dynamic weight = 1), then the witness dynamic vote = 1
  • If there are an odd number of nodes that have a vote (dynamic weight = 1), then the witness dynamic vote = 0

To check the vote status of the witness, use the Windows PowerShell command below. A return of 1 means the witness has a vote; a return of 0 means the witness doesn't have a vote.

This is a read-only value. It simply shows the vote status of the witness.

(Get-Cluster).WitnessDynamicWeight