After upgrading my server environment to Windows Server 2012 a few weeks ago, I was pleased to see that everything ran and there were no issues. However, the virtual disk format for my pre-existing VMs was still was the old VHD one. As I described in an earlier blog post.

Hyper-V 2012 supports a newer disk format known as VHDX. I wanted to get more experience using Hyper-V 2012 and also wanted the higher performance and reliability available with the new disk format, but I did not want to have to re-install and re-configure my virtual machines. Fortunately, Microsoft provides a nifty tool for managing and changing disk formats. In the Hyper-V manager, click on “Edit Disk” in the Actions section, and it brings up a disk wizard that leads you through the steps to convert a disk to a different format.  You can do the following:

  •  convert from a VHD to a VHDX — and vice-versa, though I am not sure when this would be needed, other than migrating to an earlier version of Hyper-V server.
  • expand the capacity of a virtual disk. Note that this will not expand the volume; you do that with the standard Windows Disk management tool
  • convert from a dynamic disk to a fixed disk, and vice-versa.

A dynamic disk expands as needed to store more data, i.e., even if you indicate that the disk will be 40GB in size, the VHDX file will not start out that large. It will start out small as the disk is created and grow when you add more to it. If you have a fixed disk, the VHDX file associated with this disk will be 40GB in size no matter what. There is some performance penalty in using a dynamic disk since they grow dynamically, but they are also created much more quickly and occupy the minimum amount of disk space on the host. Less frequently but sometimes used is the differencing hard disk.  These disks are a “child” to a “parent” VHDX, and provide a way to store changes in a different location than the parent.

Once I completed the Disk Wizard, I restarted my VM and everything worked great! The UEB software can back up and restore my VHDX-based VMs, so my data is well-protected.  It was such an easy process, and now I know I’m using the most up-to-date virtualization technology Microsoft offers.

Comments

  1. Great blog!!! I just recently setup my company’s private cloud using 2008 R2 and love it, but hear great things about 2012. Do you know how easy, or if I should, update my hosts to 2012? If I did, is it something I just move the VM’s off it, update to 2012, then move them back and update to VHDX?

  2. Eric,
    Thanks for the comment! In my situation, I was moving from one system (Windows Server 2008 R2) to another (Windows Server 2012), so I exported VMs from the Windows 2008 R2 system, copied and imported on the 2012 system, then upgraded to the new disk format. I have read where a lot of people have upgraded OS versions without issues, while others have seen that they had to reinstall the Hyper-V role after the upgrade. If you’re using Hyper-V 2008 R2 Server core, it cannot be upgraded to Hyper-V Server 2012. You have to do a reinstall and export your VMs to a non-system disk and import them after installation. I found some pretty useful information here:
    http://social.technet.microsoft.com/Forums/en-US/winserverhyperv/thread/bebf962f-cf29-4878-a642-b56b3c702b6f

  3. Using a standalone Hyper-V Server 2012 I don’t see the option to convert VHD to VHDX. Is this only available in Windows Server 2012 version of Hyper-V?

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