The vhdx format provides support for 2 terabyte drives, can difference dynamic disks faster and provides more options for sector sizes. When upgrading into Server 2012, you can migrate your vhd files to vhdx files using Hyper-V Manager. To do so:
You can also use the convert-vhd powershell cmdlet to covert these vhd files. It’s an easy powershell command to use. Simply specify the source as your first positional parameter and the target as the second, as follows.
convert-vhd V:\myvm.vhd V:\myvm.vhdx
The fact that you can manage these from a script also opens up the ability to automate the conversion for a number of files concurrently.
krypted March 14th, 2014