A Virtual hard disk is saved either with VHD or VHDX file extension. VHD is the older while VHDX is the newer file extension used by Microsoft Virtual PC and Virtual Server. VHD is supported by Windows 7 and earlier versions. On the other hand, VHDX is supported by Windows 8 and Windows Server 8 operating systems. VHDX has new capabilities like performance improvements, data corruption prevention mechanisms, and a 16TB maximum allowable size.
Though the new VHDX file has data corruption prevention mechanisms, it’s not completely immune to corruption. Sometimes corruption may occur and cause inaccessibility.
https://www.sysinfotools.com/blog/virtual-hard-disk-use-virtual-machines/