Windows 2012 Failover Clusters and vSphere 5.1

How many of you actually read through the release notes of a new vSphere release?  Ok, I know that Maish does.  If you read Maish’s post or read the vSphere 5.1 Release Notes you would see the following:

Windows Server 2012 Failover Clustering is not supported
If you try to create a cluster for Failover Clustering in Windows Server 2012, and select to run validation tests, the wizard completes the validation tests with warnings, and after that returns to running the validation tests again. The wizard in the Windows Server 2012 guest operating system does not continue to the cluster creation stage.

Workaround: None.

I admit I didn’t notice it myself and had it recently pointed out to me.  It’s unfortunate that this piece of information is buried in the Release Notes and not listed in the VMware Knowledgebase, the vSphere 5.1 Clustering Guide, etc.  Despite the fact that many in the industry despise virtualized Windows Failover Clusters, the fact remains that organizations use them and will continue to use them.  vSphere HA can sometimes serve as a replacement but not always.  More on my thoughts on this subject here.

To make sure everyone understands the issue here – when creating a Windows Failover Cluster, you can run through a validation process to make sure the cluster will function properly.  Microsoft will only support a cluster (virtual or physical) if it has been validated.  As you can see in the Release Notes, it appears that Windows 2012 Failover Clusters do not successfully complete the validation step.

I figured I’d give this a try and see if I can reproduce the issue and to my surprise I cannot.  I’ve tried the traditional method of clustering virtual machines by using RDMs in physical compatibility mode.  I’ve also tested using storage presented via the iSCSI initiator inside the virtual machine.  In both cases I was able to validate the cluster and receive a validated rating that is good enough to qualify for Microsoft support.


I’m not sure what the actual problem is with Windows 2012 Failover Clusters but I’m unable to reproduce the behavior listed in the Release Notes.  The behavior described in the Release Notes is what happens when the cluster fails the validation test and is actually expected.  If your cluster passes the validation tests, as mine did in the tests I ran, it proceeds to create the cluster without an issue.

Hopefully VMware will clarify this issue for us and/or change their support stance.  I firmly believe you should stick with what is supported when virtualizing business critical applications.  In this case I can’t even figure out why it isn’t supported in the first place, but do have to recommend that organizations hold off on virtualizing Windows 2012 Failover Clusters until this support statement is changed.

Anyone else tried to virtualize a Windows 2012 Failover Cluster and see the behavior that VMware describes?

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7 thoughts on “Windows 2012 Failover Clusters and vSphere 5.1

  1. Thanks for your article. That’s really a piece of information that can be overread very easily. Do you have any information if a Windows 2012 Failover Cluster is supported under vSphere 5.0 (ESXi500-201209001 5.0.0 Patch 8, 2012-09-27, Build 821926)?
    I installed a Failover Cluster in my lab today and it worked without any problems.

    Thanks and regards


    1. Hey Michael,

      Thanks for the comment. Based on VMware’s Compatibility Guide, Windows Server 2012 is fully supported on ESXi 5.1 and ESXi 5.0 Update 1 (see here: . I would make sure you’re running Update 1 in order to have full support.

      As for whether or not it will work or is supported, that’s sort of up in the air based on this post. VMware says it is unsupported but I have only seen the issue reproduced using the “cluster in a box” solution where all virtualized cluster nodes are confined to a single ESXi host. Since that configuration is not one I’ve seen used in production it doesn’t really concern me. For all other configurations that I tested above I had no issues.

      It’s a shame that support isn’t officially there yet because Windows Server 2012 Failover Clusters work great and are a lot easier to setup and manage than previous versions..

      Good luck with your testing!


  2. Hi Matt
    Thanks For the info . I to have installed a test environment Clustering on a single host (ESXI 5.0 update) and past the validation test successfully. but when i create the disk its read only.any suggestions on how to gine R/W ?

    1. Hey Meron,

      I’m not sure exactly why your shared disk is showing up as read-only. If I had to guess I would think that some step in the clustering guide was missed. I’d suggest starting over and going through each step again to make sure you didn’t miss anything.

      Sorry I don’t have a more definitive answer for you. Unfortunately in my experience with virtualizing clusters I haven’t run into that particular issue.


  3. Hi,

    is the Windows Server 2012 Failover Cluster still not supported from VMware?
    Or did they change it over the time?


    1. Hi Nic,

      Thanks for the comment. Right now the only supported method of running a Windows Server 2012 Failover Cluster is by using either non-shared storage clustering solutions (such as Exchange 2010 DAGs or SQL Server 2012 AAGs), or by using in-guest iSCSI or SMB access to shared storage. In the in-guest storage scenario, you present storage to your virtual machine via the guest iSCSI initiator taking vSphere completely out of the storage stack. That specific configuration is supported (and has been for quite some time with other Microsoft clustering solutions).

      The following KB has been updated recently to reflect that change:

      Finally, though I can’t comment on features in the next release of vSphere, I would expect better support for Windows Server 2012 Failover Clusters in future releases of vSphere.. 🙂


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