Q. If I have a differencing Virtual Hard Disk (VHD), can I modify its parent VHD?

A. No. Once a VHD has differencing VHDs created from it, it becomes a parent VHD and no changes should be made to it. Changing the parent would invalidate the state of the differencing (child) VHDs. The modification date of the parent VHD is stored in the differencing VHDs and is checked when the differencing VHD is used. If the modification date on the parent doesn't match the date in the differencing VHD, the differencing VHD won't be usable.