Extend Hyper-V Guest System Partition

A co-worker messaged me today to ask for my help in giving one of our development domain controllers some additional disk space.  Due to space constraints and lack of funding I had to get creative last year in redesigning our development environment to handle four more servers for a new application with no new hardware.  I had 3 physical servers so here is how I set them up.  The first runs Hyper-V with four VMs that are our domain controllers.  The second and third servers run VMWare VSphere and each host two virtual machines for the new application.  The server he needed to get additional space on was our domestic domain controller running in Hyper-V.

CAUTION!!!!

I highly suggest that you make a copy of your VHD file after you shut the guest machine down.  Backups are Gold!

Prepare the Guest

Your first step is to shut down the guest machine.  Next you need to increase the virtual disk so it will be presented to the guest when you turn it back on.  It’s very simple and here is how:

1. Open Hyper-V Manager
2. Select the desired Hyper-V server in the left pane
3. Select the desired virtual machine in the center pane
4. Select Edit Disk in the right pane
5. The edit virtual disk wizard opens. Select next on the welcome page
6. On the Locate Disk page click browse and select the virtual disk for your virtual machine
7. On the Action page select Expand
8. On the Configure Disk page change the disk size to the new desired size. Current and maximum sizes are provided in the window.

Prepare the VHD

We are going to use the tried and true diskpart.exe to expand the disk.  Remember that this is a system partition and the general rule is that system partitions cannot be expanded without a third party tool.  Let’s prove them wrong by using diskpart on the drive while the OS is not running.  There are three ways I can think of to do this.  The first is booting the machine to floppy and running diskpart from there.  I know this can be done, but I personally have never been successful and have turned to third parties for the solution.  However, this is a virtual machine and not physical so I have other means of running diskpart on the drive without the OS running.  That leads me to the second option of attaching the drive to another virtual machine as a secondary drive.  You could then run diskpart on that partition from the other virtual machine.  The third option is what I used and will describe here.  It should be noted that Windows Server 2008 and Windows 7 can mount VHD drives natively and will not require the tool I will be using.  Here’s how we do it:

1. Download Virtual Server 2005 R2 SP1 from HERE
2. Install Virtual Server using the custom option and select ONLY the VHD Mount
3. Open a command prompt
4. Type vhdmount /p /f <Fully Qualified Path to your VHD File>
5. Type diskpart.exe
6. Type List Volume
7. Type Select Volume <2 or whatever volume number is your VHD>
8. Type Detail Volume to verify the free space and that your selected the correct drive
9. Type Extend
10. Type Detail Volume to verify the free space is now zero and the size is what you expect
11. Type Exit
12. Type vhdmount /u <Fully Qualified Path to your VHD File>

Start up your virtual machine and you should now see your boot partition extended!