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I'm new to hyper-v, and I'm wondering how to do the following : I'd like to have an image of fresh install of windows, and create a 'differencing' disk with some apps.

Can I then modify the parent hard drive, to install updates ? Will they be included in the child hard drive ?

The other solution would be to copy the "fresh windows" hard drive, but it will use much more space, and I'll have to download windows updates multiple times.

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I've never used Hyper-V, but I run Virtualbox and the solution seems to be the same. http://technet.microsoft.com/en-us/library/dd560637.aspx describes the "snapshot" functionality, which is just the "differencing disk" you're looking for. However, (in Virtualbox anyway) you can't edit the parent hard drive and have the snapshot offspring work correctly, to my knowledge.

Edit:

Taking a checkpoint/ snapshot of a VM is like using a parent disk - all the changes to a VM after a snapshot is taken are written to a new VHD (You’ll see this on your physical disks with a .AVHD extension where you specified to save your snaphots). If I create a subsequent snapshot then another AVHD is created and changes are then written to this newer AVHD file.

(Source)

As I thought, Hyper-V works exactly like my VirtualBox snapshots, it freezes the source virtual drive and writes all changes to a separate "differencing" file. You can't edit the parent at all once you've made a snapshot, unfortunately (the snapshot will break).

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From what I've read so far, snapshot allow you to quickly come back to a previous state of the hard disk. –  Manu Feb 4 '13 at 14:05

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