Shut down the virtual machine and convert the VHD-format dynamic virtual hard disk to a VHDX-format virtual hard disk or ...

Shut down the virtual machine and convert the VHD-format dynamic virtual hard disk to a VHDX-format virtual hard disk or to a fixed virtual hard disk. (The VHDX format has reliability mechanisms that help protect the disk from corruptions due to system power failures.) However, do not convert the virtual hard disk if it is likely to be attached to an earlier release of Windows at some point. Windows releases earlier than Windows Server 2012 do not support the VHDX format.