The only traces of the technical preview installation when you choose the "boot to VHD option" are the VHDX file itself and the boot menu option. No repartitioning, reinstallation or anything else is necessary.
I think this preview supports the premise of what we have come to expect from the Windows Server team over the past few years -- lots of great, measured, steady progress across the breadth of the product. There is not a whizbang "buy me now" feature in Windows Server 10, or at least there is not yet. Rather, what we see is a competent, capable server OS taking its next steps into making its technologies available more easily and more scalably.
Windows 10 on the client side has a lot to answer for, given the panning of Windows 8 by large swaths of the Microsoft user base, but on the server side, Windows Server 10 seems in this preview release like a very solid march forward on all fronts.
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