By Michael / Last Updated May 12, 2023

Need to extend Hyper-V guest system partition

Nowadays, many users set up a virtual machine such as Windows Server 2008 (R2), Windows Server 2012 (R2), Windows Server 2016 or 2019 running on Hyper-V. Hyper-V can create virtual machines on x86-64 systems. What’s more, a host server running Hyper-V can be accessed remotely by multiple guest computers. Each guest computer could perform as if they are using the host server directly. Users on the guest computers could run programs in the host server remotely, even though that program is not available on the guest computer.

However, as time goes by, users found that system partition had run out of space, then the Hyper-V will run slowly gradually. Therefore, how to extend Hyper-V system partition?

Tutorial: expand Hyper-V boot partition

If you know more about Hyper-V, you should know basic steps: first extend the virtual hard disk using Hyper-V, then extend system partition inside the VHD.

Before you do, please pay attention to:
First completely shut down the virtual machine because you cannot extend a virtual hard disk that is associated with a running or saved stated virtual machine.
Remove the saved snapshots of the Hyper-V. If you expand a virtual hard disk that is associated with a virtual machine that has snapshots, these snapshots will be invalidated.
After expanding the virtual hard disk, there will be an empty space at the end of the virtual hard disk. You will try to expand system partition using this unallocated space.

Part 1: extend Virtual Hard Disk (VHD)

At first, we highly suggest you make a backup of your VHD file after shutting the guest machine down.

Hyper-V VM

Secondly, open Hyper-V Manager and select the desired Hyper-V server, here, we take Windows Server 2008 as an example -> Select desired virtual machine in the center panel -> Select Edit Disk. Click Next to go, then browse and select the virtual disk on the Locate Disk page -> On the action page, please choose Expand.

Expand Virtual Disk

Then, type a new size and click finish.(Current and maximum sizes are provided in the window)

Input Disk Size

Thus Part 1 is almost finished. Start your VM and open computer Management - Disk Management, you will see there is an unallocated partition at the end of the disk because vhd size has been expanded. Now our task is to extend system partition.

Part 2: Extend system partition within the Hyper-V machine

In the Disk Management, you can use the “Extend Volume” feature to add the unallocated space into the system partition only when it is right after the C drive. Namely, it only works there is only one partition (C:) on the virtual hard disk. If there are some other partitions in the way of the system partition and the unallocated space, the “Extend Volume” will be greyed out and disabled (as the screenshot is shown).

Extend Volume Greyed Out

Then what you should do to extend Hyper-V guest system partition? Luckily, you can turn to AOMEI Partition Assistant Server Edition. It is specially designed for Windows Server operating system, including Windows Server 2003, Windows Server 2008 (R2), Windows Server 2012 (R2), Windows SBS, Windows Server 2016, Server 2019 and Windows PC,

Its “Merge Partition” feature can directly merge non-adjacent unallocated space into C drive or some other partitions by 3 steps. Next, let’s see how to use it to extend Windows Server system partition quickly. (PS.: you can download the Demo version for a free trial.)

Download DemoServer 2012/2016/2019/2022
Secure Download

Step 1. Install and run the software. Right-click C: drive, choose “Advanced” and select “Merge Partition”

Merge Partitions

Step 2. In the pop-up window, tick the unallocated partition and click “OK”.

Tick Unallocated Space

Step 3. In the main screen, click “Apply” to commit the pending operation.


See? Just with three steps, you can easily expand the Hyper-V guest boot partition. Besides, this versatile software can also move partition to make the unallocated space next to the aim partition you wish to extend.


After reading this article, I am sure you know how to extend Hyper-V guest system partition now. The above software-AOMEI Partition Assistant Server is a great disk partition manager for Windows Server and PC users. If you want to clone Windows Server to SSD, allocate free space from one partition to another, align SSD partitions, recover lost partition, and more, it can also satisfy you well.