Hyper-V>> Save diskspace using a differencing disk

In the last blog, there is explained how to create a virtual machine. In this blog we'll talk about creating a differencing disk. 

What is a differencing disk?

A differencing disk is a disk that's based on a so called parent disk. This parent disk can be a sysprepped image of Windows 7/8/2008/2012 or another OS. It can also be just a plain simple image of another machine. The differencing disk uses this parent disk, and saves only the differences in it's own disk. This way you can create lots of machines that are based on the same parent disk. The performance will be a little less good then normally, but it's still workable. However, because you'll need less snapshots and initial disks, the free disk space on your storage will be better. The snapshots you will make will also be smaller. 

How do I create a differencing disk?

1. First, make a new VM. See my previous blog for the steps that need to be taken to achieve this.

2. Give the VM a fitting name.

 

 

3. Choose 'Attach a virtual hard disk later' and finish the wizard.

 

 

 

4. You will return to the Hyper-V Manager. Right click, and choose Settings. THe screen below will appear. Go to IDE Controller 0 in the left pane, and click on Add.

 

 

 5. You will see the following screen. Now click on New.

 

 

 6. Click Next. The following screen will appear. Choose VHDX. Take notice that this format is only compatible with Windows 8 and newer.
 7. Click Next again, and now you can choose the type of disk. Choose for differencing disk.
 

 

 

8. Give the disk a recognizable name, and click on Next. 

 

 

9. Choose the parent disk in the next screen. In this particular case, I've chosen a sysprepped Windows 7 disk.

 

 

 

10. Click again on next, and check the summary to see if everything is OK. When this is the case, click Finish. 

 

Note: You can check if the disk really is a differencing disk using Powershell. You can also check this in the properties of the disk.