1.2 – Creating and Configuring Differencing Disks (Hyper-V)

Overview

This lab demonstrates how to create and manage Hyper-V differencing disks using a generalized parent disk. The objective is to optimize storage usage and deployment time in a testing/lab environment by reusing a single parent VHDX and creating child virtual machines based on it.

This lab also covers merging a differencing disk to break its dependency on the parent disk.

Environment Information

Item Value

Host OS Windows

Hypervisor Hyper-V

Parent VM Name Parent

Child VM Name MGMT

Parent Disk Name Parent.vhdx

Disk Type VHDX – Dynamic

Disk Size 200 GB

Windows Version Windows Server Datacenter (Trial)

Task 1: Create Parent VM and Parent Disk

Step 1: Create Parent Virtual Machine

Open Hyper-V Manager

Click New → Virtual Machine

VM Name: Parent

Generation: Generation 2

Startup Memory: 4 GB

Network: Default Switch




Step 2: Create Parent Virtual Disk

Disk Format: VHDX

Disk Type: Dynamic

Disk Size: 200 GB

Disk Name: Parent.vhdx



Step 3: Install Windows Server (Fresh Install)

Attach Windows Server Datacenter (Trial) ISO

Start the Parent VM

Perform a clean installation

Log in and reach the Windows desktop


Step 4: Fully Patch the Parent Server

Open Windows Update

Install all available updates

Restart as required

Verify the system is fully up to date



Step 5: Run Sysprep

What is Sysprep?

Sysprep (System Preparation Tool) is used to generalize a Windows installation by removing system-specific identifiers such as SIDs. This allows the operating system image to be safely reused for multiple virtual machines.

Steps:

Navigate to C:\Windows\System32\Sysprep

Run sysprep.exe

Select Out-of-Box Experience (OOBE)

Check Generalize

Set Shutdown after completion


Step 6: Delete Parent VM (Keep Disk)

Right-click the Parent VM

Select Delete

Confirm that Parent.vhdx was not deleted



Step 7: Set Parent Disk to Read-Only

Right-click Parent.vhdx

Open Properties

Enable Read-only


Task 2: Create Differencing Disk and Child VM

Step 8: Create Differencing Disk

Select New → Hard Disk

Format: VHDX

Disk Type: Differencing

Disk Name: MGMT_Diff.vhdx

Parent Disk: Parent.vhdx


Step 9: Create Child VM Using Differencing Disk

Create new VM named MGMT

Generation: Generation 2

Attach MGMT_Diff.vhdx

Start the VM

Explanation

Differencing disks store only the changes made to the child virtual machine while the parent disk remains unchanged. This approach significantly reduces storage usage and deployment time. Differencing disks are recommended for testing and lab environments only, not for production use.

Task 3: Merge Differencing Disk (Break Parent Dependency)




Step 10: Shut Down Child VM

Fully shut down the MGMT virtual machine


Step 11: Merge the Differencing Disk

Open Edit Disk

Select MGMT_Diff.vhdx

Choose Merge

Select Merge to a new disk

Specify a new VHDX name



Step 12: Attach Merged Disk

Remove the differencing disk from the VM

Attach the merged VHDX

Start the MGMT VM



Final Summary

In this lab, a parent virtual disk was created and generalized using Sysprep. A child virtual machine was then deployed using a differencing disk to optimize storage usage. Finally, the differencing disk was successfully merged into a standalone VHDX, removing its dependency on the parent disk. This lab demonstrates efficient virtual machine deployment techniques suitable for testing and lab environments.

Screenshots

Screenshots for each major step are stored in the /screenshots directory and referenced in this repository.

Notes

Differencing disks should never be used in production environments.

The parent disk must remain unchanged and read-only while differencing disks are in use.