We are great fans of virtual machines here at G2 and we regularly use both VMWare and Windows Hyper-V to virtualise devices, particularly old legacy servers. Both VMWare and MS provide the ability to create snapshots of virtual machines, effectively saving the state of a virtual machine and it’s hard disks at a given point in time.

With MS Hyper-V there are times when you need to manually merge a snapshot back in to it’s parent HD. This is really simple, but be prepared with a cup of coffee as it can take a while.

1) Firstly navigate to the folder containing your snapshots. By default this is;

C:\ProgramData\Microsoft\Windows\Hyper-V\Snapshots

Find the snapshot folder you are interested in. Inside the folder will be a snapshot differencing file with the extension .avhd. Change this extension to .vhd.

2) Open Hyper-V Manager and click Edit Disk from the right-side nav bar

Select Edit Disk

 2) Select Next at the introduction screen.

Introduction

3) Select the file you renamed in step 1. Click Next.

Select VHD file

4) Select the option to merge. This will merge the snapshot with the parent VHD hard disk. You will need sufficient disk space for the resulting file. A good rule of thumb is that you will need enough temporary space for both files added together. Click Next.

Choose Merge

5) The merge will start. This can take some time (we recently merged a 100GB VHD with a 60GB snapshot and it took several hours).

Waiting to merge

That’s it. When the merge has completed you’l be able to fire up your VM in Hyper-V Manager.