Hyper-V Failover Clustering, Beyond the Z Drive using the disk GUID

Are you running Hyper-V?  Have you used up all the available drive letters deploying LUN’s for VM’s in your Failover Cluster?  Running out of drive letters? It is fairly easy to get around the 26 drive letter limit in windows when deploying VM’s in a Hyper-V failover cluster configuration.  It is possible to deploy 2000 LUN’s to your Hyper-V cluster environment allowing you to grow your cluster and take advantage of your hardware.

In order to grow beyond the 26 drive letters you will need to install HotFix KB951308.  Once this hot fix is installed you can create shared storage using the drives GUID rather than drive letter or mount point.  Using the drives GUID you can create up to 2000 shared volumes without worrying about running out of identifyers.

What you need to do:

  • Install hotfix KB951308 on all hosts in the Hyper-V Failover Cluster
  • Reboot your Hyper-V hosts
  • Present storage to the server
  • Bring the new storage on-line
  • Initialize the new storage
  • partition and Format the storage, but don’t assign a drive letter or mount point

Using he command mountvol.exe from the command line you can view the GUID for all storage devices attached to your system.  NOTE: You need to run this command form the server that currently owns the storage resource that you want to locate the GUID for.  Alternatively you can locate the GUID by right clicking the storage device in Failover Cluster Manager and selecting properties.


Once you have the GUID for the volume you would like to deploy your new Virtual Machine to do the following:

  • Launch the new virtual machine wizard using Hyper-V manager
  • On the “Specify Name and Location” step check the box next to “Store Virtual Machine in a different location” and paste the volume GUID in the location box.
  • On the “Connect Virtual Hard Disk” step choose “Create a Virtual Hard Disk” and in “Location” box paste the GUID for the volume.
  • Complete the creation of your Virtual Machine

Once your Virtual Machine is created you need to launch “Failover Cluster Manager” and create a new “Virtual Machine” Service.  When you create the new Virtual Machine service the disk will automatically be added as a resource for the Virtual Machine”

You can also acheive this using SCVMM 2008.  Make sure to deploy the new VM on the server that currently owns the disk resource.