Hyper-V has a very interesting feature that allows to save a lot of space: By creating a golden VHDX Disk with the base operating system, you can then use so called “Differencing” disks, which reference the Master VHDX and only save the changes on their disk.

So, first things first: Just create a normal VM to prepare the golden image for later use.

Hyper-V Specify Name and Location

Specify Generation 2

Hyper-V specify VM generation

Give the Golden disk a self-explanatory name

Hyper-V Connect Virtual Hard Disk

Before starting the VM, disable automatic checkpoints (in VMware known as Snapshots) and give it more juice. Do not forget to apply changes:

Hyper-V VM Settings-Checkpoints
Hyper-V VM Setting Processor

Install the OS (standard procedure)

Once the OS installed and custom settings are made, the machine is ready to be Sysprep’ed.

Windows+R sysprep

Delete the VM once stopped, the disk will not be deleted. Then locate the VHDX and set it into Read-Only mode.

Hyper-V delete Virtual Machine
File Properties

Now a new VM can be created in Hyper-V with a Differencing disk. Note: In the VM creation wizard specify “Attach a virtual disk later”:

Attach a virtual Disk later

Now in the VM settings under SCSI Controller add a new Hard Drive:

Hyper-V VM Settings New Hard Drive

Select the last option for Differencing:

Differencing Disk

This will be the new disk name:

Hyper-V New Disk Name

And finally, the base disk we created previously:

Specify Parent Disk

Before powering on the machine make sure the new disk is first in the boot order.

Hyper-V VM Settings Boot Options

The VM is up and running!

Windows Server 2019 Settings

Notice the size of the new VHDX. Only 1.4 GB!

Windows Explorer File Size

In the VM settings you can once again inspect the disk and see the relationship with the golden disk.

Hyper-V Inspect Hard Drive
Hyper-V Virtual Hard Disk Properties
Hyper-V Virtual Hard Disk Properties