By Catherine / Last Updated October 28, 2019


First, let me make clear that this article is based on Hyper-V 2.0 (Windows Server 2008), these steps may not work for Hyper-V 3.0 (Windows Server 2012). For information on Windows Server 2012 (R2), please visit one of my other posts.

Why do you need to increase the virtual disk size in Hyper-V (Windows Server 2008)?

Have you ever experienced the “out of Disk Space on Drive C” error message on your Virtual Machine running Windows Server 2008 (R2)? If yes, then this article can help you!

First, we will increase the virtual disk size at the hardware level – the VMs .vmkd file – once this is completed will we enter the VM to make the necessary changes through the OS’s GUI. This will allow us to take advantage of the additional space that has been provided by the hard disk having been extended.

There are two main parts to the process. First, we need to make the VHD bigger and second we should extend the system partition to take advantage of the new space.

The way to increase the virtual disk size in Hyper-V (Windows Server 2008)

Part I - Increase Virtual Disk Size

Shutdown the server, open Hyper-V Manager and select ‘Edit Disk’. In the welcome screen click ‘Next’ and then click on the file path of the VHD that you want to increase the size of and then click ‘Next’ again. You will now be on the ‘Choose Action’ window, you should select ‘Expand’, and then click ‘Next’. When prompted, enter the new size of the virtual disk, and click ‘Next’ once more. In this example I used a VHD which had 648.45 GB and I increased it to 698.49 GB.

Choose Action

Choose Action Page

Edit Virtual Hard Disk

Expand VHD page

You can also use a PowerShell script if you need to automate the process. For information on the PowerShell script, please search on Google, as to save space I will not explain it here.

Part II –Extending the ‘C Drive’ to use the unallocated capacity on the VHD

Once the virtual disk size has been increased at the hardware level (as mentioned in the previous part) you will now be ready to extend the system partition through the Windows GUI. The process is simple and will only require a few clicks.

Extend Volume is grey

Open the Windows Server 2008 built-in Disk Manager and right click on the ‘C Drive’, unfortunately you may find that the ‘Extend Volume’ option is invalid.

If it is then unfortunately it won’t be just a few mouse clicks! Luckily, AOMEI Partition Assistant Server Edition - specialist third-party partition manager - will allow you to easily extend the system partition!

Install and run the program. Right click the ‘C Drive’ and select ‘Merge Partitions’.

Merge Partitions

In the pop-up window, check the ‘unallocated space’ option and click ‘OK’ to go back the main window.

Tick Unallocated Space

Here you can see that some changes have been made – notably that partition C has become much larger. AOMEI Partition Assistant has successfully allowed to you avoid several laborious steps (moving and resizing the partitions). AOMEI Partition Assistant is a far more powerful tool that Windows Server Disk Management and it allows you to simply click ‘Apply’, and then sit back and wait for the “out of Disk Space on Drive C” error to disappear.


More about AOMEI Partition Assistant

In this tutorial, we see AOMEI Partition Assistant Server Edition work perfectly on Window Server 2008 to solve the “out of Disk Space” error.

In fact, AOMEI Partition Assistant Server Edition serves as a versatile professional partition tool which works well on all Windows Server operating systems (Windows Server 2012 (R2), Windows Server 2008, Windows Server 2003, and it also works well on Windows XP, Window Vista, Windows 7, and Window 8/8.1.) AOMEI Partition Assistant Server Edition has the functionality to create partition, copy partition, split partitions, convert partition styles, and more. Windows Disk Manager can be entirely replaced by the far more user friendly AOMEI Partition Assistant.