Cluster Quorum witness

Introduction

Since W2012R2 it is recommended that all clusters have a quorum witness regardless of the number of cluster nodes. As you may know, the purpose of the cluster witness is to ensure a majority vote in the cluster. If you have 2 nodes with one vote each and add a cluster witness you create a possibility for a majority vote. If you have 3 nodes on the other hand, adding a witness will remove the majority vote as you have 4 votes total and a possible stalemate.

If as stalemate occurs, the cluster nodes may revolt and you are unable to get it working without a force quorum, or you could take a node out behind the barn and end its misery. Not a nice situation at all. W2012R2 solves this predicament by dynamic vote assignments. As long as a quorum has been established, if votes disappear due to nodes going offline, it will turn the witness vote on and off to make sure that you always have a possibility for node majority. As long as you HAVE a disk witness that is.

There are three types of disk witnesses:

  • A SAN-connected shared witness disk, usually FC or iSCSI. Recommended for clusters that use shared SAN-based cluster disks for other purposes, otherwise not recommended. If this sounds like gibberish to you, you should use another type of witness.
  • A File share witness. Just a file share. Any type of file share would do, as long as it resides on a Windows server in the same domain as the cluster nodes. SOFS shares are recommended, but not necessary. DO NOT build a SOFS cluster for this purpose alone. You could create a VM for cluster witnesses, as each cluster witness is only about 5MiB, but it is best to find an existing physical server with a high uptime requirement in the same security zone as the cluster and create some normal SMB-shares there. I recommend a physical server because a lot of virtual servers are Hyper-V based, and having the disk witness on a vm in the cluster it is a witness for is obviously a bad idea.
  • Cloud Witness. New in W2016. If you have an Azure storage account and are able to allow the cluster nodes a connection to Azure, this is a good alternative. Especially for stretch clusters that are split between different rooms.

How to set up a simple SMB File share witness

  • Select a server to host the witness, or create one if necessary.
  • Create a folder somewhere on the server and give it a name that denotes its purpose:
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  • Open the Advanced Sharing dialog
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  • Enable sharing and change the permissions. Make sure that everyone is removed, and add the cluster computer object. Give the cluster computer object full control permissions
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  • Open Failover Cluster manager and connect to the cluster
  • Select “Configure Cluster Quorum Settings:
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  • Chose Select The Quorum Witness
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  • Select File Share Witness

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  • Enter the path to the files share as \\server\share

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  • Finish the wizard

  • Make sure the cluster witness is online:

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  • Done!

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  1. jeankadang’s avatar

    Hi

    just a quick heads-up

    you’ve censored the server name (dc03) in one picture (second from the bottom) – but not in the final picture 😉

    Reply

    1. DizzyBadger’s avatar

      Thanks for the heads-up. This is from a lab setup, but best to be consistent 🙂

      Reply

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