While we are waiting for Windows server 2012 R2 I just played with a feature that will come very useful after upgrading Hyper-V hosts to new version (R2). Microsoft did a great job with the possibility to live migrate (by using shared nothing live migration feature that was already available in Windows server 2012) from old Windows server 2012 hosts with Hyper-V to new Windows server 2012 R2 hosts with Hyper-V. So you will have zero downtime while upgrading your virtualization platform. This goes one way only – so only from older (Windows server 2012) to Windows server 2012 R2 and NOT vice versa.
Here is a video how it works – at the end I also demonstrated that it does not work in opposite direction.
http://screencast.com/t/yz0ggCbFki
Update: It will fail if you have different name for virtual switch – If you have a new name for virtual switch on new server I suggest that you create an “fictive” private virtual switch with the same name on original (old hyper-v). You are not able to choose virtual switch on destination.
Luka Manojlovic 
Hi!
I moved few machines from 2012 to 2012R2 Server, few moved without problems, but on one I had so much problems, it wos so complicated to install the new integrated services. After install of the integrated services the NIC driver was not found, so I had to install them manual.
One hour to install the NIC driver !!!
After install of the driver, it was not possible to set static IP, after reboot the vm set the IP settings to default (dhcp).
So I had to delete the NIC (from the vm config), also the registry keys!
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParametersAdapters {GUID}
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParametersInterfaces{GUID}
After shutdown I have added new NIC’s to the VM and started!
The NIC were found and I set the static IP’s
regards
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Was it Windows server 2012 servers (guest VMs)?
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