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I've recently installed Windows Server 2012 to my test server to run Hyper-V test environment. I have bunch of old VMs which were created in Windows Server 2008 R2 Hyper-V which I didn't export in advance - I just have all VMs files created on old server. I was able to successfully import VMs with fixed VHD, but unable to do it with those which use differencing disks - import wizard unable to handle this. Most of my old VMs using differencing disks tied to one parent VHD.

Any advice on how to import them into Hyper-V 3.0?

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I believe you should be able to merge the differencing disk into a new disk. Then use that new disk with the VM. – joeqwerty Mar 15 '13 at 10:59

Don't think you can import differencing disks. For this disk type, differences are stored in the differencing disk, which starts with no data, and grows to store the unique data. The parent disk also will have lots of Input operations because it is the source or common denominator. This is not suitable for personal/assigned VDI VMs or server VMs because you cannot upgrade/resize the parent and inherit the changes; you have to delete the lot and start again. As a general best practice, always backup your VMs before making configuration changes. Please check out for effective Hyper-V backup.

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Looks like everything works through Import out-of-box in Hyper-V 3.0, may issues was because I've moved folder with parent disks... If everything in its place Hyper-V is picking up location of parent from VM config... The only extra thing required is reassign new NIC i.e. connect your legacy VMs to virtual switch, which is handled by Import wizard and upgrade Integration tools.

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we used this tool to accomplish the same task as you describe:

I don't think there's a way around it since the differencing disks appear to reference the old system. when you use a backup tool it reimports the VM into Hyper-V Manager

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