Windows 10: Video: Hyper-V Differencing Disks

Last Saturday, 8th of December, we had one of our TenForums Live webcasts. The topic was Hyper-V, and I had prepared a presentation / demonstration about how to use Differencing Disks to save both storage space and time.

Although the webcast was recorded, it was too hard to edit the footage because lots of on & off topic chat going on, questions and answers and so on. I decided to make a "clean" capture instead of posting that video.

You geeks who participated, please do not take this wrong; it is completely OK to chat and interrupt presentations with clarifying questions. I just thought that the topic is important, and wanted to make a bit better video.

[youtube]jKFQuBv9kbM[/youtube]

Video description on YouTube:

Originally posted in TenForums Video thread.



:)

 

Differencing Hard Disk - Hyper-V


I followed later part of this guide which says mount differencing drive and use bcdboot to add a boot entry but it would not let me mount it as a drive saying it was in use.

Windows 8 Boot to Differencing VHD


PS - as we know, it is a good idea to create base vhd in Hyper-V first so it has the hidden efi partition as well so vhd can be used on hyper-V as well.

 

Differencing Hard Disk - Hyper-V


I came across this option when creating a new had drive in Hyper-V.

Has anybody ever used one - is it analogous to e.g. a checkpoint, or an incremental image backup in Macrium Reflect?

When and how would you use it?





Edit - been reading up on it and they look quite cool for a test environment.

It is rather like a Macrium Differential image ie it contains all the changes from base version.

So you could have a base install, do a cumulative update in a differencing drive, test it, and if ok, merge the results (to original or new drive).

If you decide to discard the differencing drive you simply delete it and set the base drive as the drive in hyper-v.

Of course, you cannot modify the base drive and keep a differencing drive based on earlier version of base image.

One cool thing I see is ability to have a base image, then sysprep to a differencing drive, and then merge the base and differencing drive to a new drive.

One weakness dynamics vhds have is they grow as you do updates, but even if you delete stuff using disk cleanup, you cannot physically recover the space even if you use powershell shrink commands.

The usual solution is to copy partitions to a new vhd using tools like Minitool Partition Wizard or Macrium Reflect adjusting sizes to recover space.

I am hoping that if you merge a base and differencing drive to a new one, space is optimally recovered. My project this week :-D

 

Differencing Hard Disk - Hyper-V

Thanks Kari, as you say I got the gist of it. One thing is evident (and articles said this) is that you do need to do it really on an ssd as hdds are not really fast enough.

May I suggest that this might make an interesting topic at the next TF Live session?

If I understand the articles I read, you can do similar with vhds mounted on host but you have to use powershell commands rather than the Hyper-V gui to create differencing drives etc.

I like the idea of this as I sometimes use dism to install Insider versions to a dual boot vhd, and it would be nice to use differencing drives there as well. It is a pity you cannot upgrade W10 builds in a vhd on a host pc (easy enough to use Hyper-V).