I also discovered just a few days ago the problem that sparse VHD/VHDX image files are not being accepted by Windows.
It appears that qemu-img on Windows always tries to create images as sparse files. Only in some cases (e.g. when operating on a NTFS file system) will the file actually be a sparse file. Being a sparse file seems to be no issue when using these file with QEMU itself. Most file formats that qemu-img is able to create will be unknown to Windows own tools, but the one exception are VHD/VHDX files. As long as a file carries the sparse attribute it will be "un- acceptable" to the Windows tools (e.g. diskpart/diskmgmt). As a crude work-around I've noticed that a copy of such a file will have "lost" the sparse attribute, and therefore can be mounted. Likewise any copy of a file created on a different system will not be a sparse file (and hence the issue does not arise). I'm attaching a log file (with a few comments) of some steps that demonstrate the problem, and how I worked around it. The test was done with qemu-img v4.1.0, but I'm fairly certain that this issue has been present since "forever" (and a quick re-test with v4.2.0 confirmed that it has not "gone away"). So, a simple work-around exists, but I see myself unable to suggest a patch. I guess the patch should be specific to prevent the creation of sparse VHD/VHDX files on Windows. But from the superficial reading I did I could not work out whether the image format information would be available in 'raw_co_create()' (of: 'block/file-win32.c'). ** Attachment added: "sparse-VHD_issue.log" https://bugs.launchpad.net/qemu/+bug/1759522/+attachment/5332081/+files/sparse-VHD_issue.log -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1759522 Title: windows qemu-img create vpc/vhdx error Status in QEMU: New Bug description: On windows, using qemu-img (version 2.11.90) to create vpc/vhdx virtual disk tends to fail. Here's the way to reproduce: 1. Install qemu-w64-setup-20180321.exe 2. Use `qemu-img create -f vhdx -o subformat=fixed disk.vhdx 512M` to create a vhdx: Formatting 'disk.vhdx', fmt=vhdx size=536870912 log_size=1048576 block_size=0 subformat=fixed 3. Execute `qemu-img info disk.vhdx` gives the result, (note the `disk size` is incorrect): image: disk.vhdx file format: vhdx virtual size: 512M (536870912 bytes) disk size: 1.4M cluster_size: 8388608 4. On Windows 10 (V1709), double click disk.vhdx gives an error: Make sure the file is in an NTFS volume and isn't in a compressed folder or volume. Using Disk Management -> Action -> Attach VHD gives an error: The requested operation could not be completed due to a virtual disk system limitation. Virtual hard disk files must be uncompressed and uneccrypted and must not be sparse. Comparison with Windows 10 created VHDX: 1. Using Disk Management -> Action -> Create VHD: File name: win.vhdx Virtual hard disk size: 512MB Virtual hard disk format: VHDX Virtual hard disk type: Fixed size 2. Detach VHDX 3. Execute `qemu-img info win.vhdx` gives the result: image: win.vhdx file format: vhdx virtual size: 512M (536870912 bytes) disk size: 516M cluster_size: 33554432 Comparison with qemu-img under Ubuntu: 1. Version: qemu-img version 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.16), Copyright (c) 2004-2008 Fabrice Bellard 2. qemu-img create -f vhdx -o subformat=fixed lin.vhdx 512M Formatting 'lin.vhdx', fmt=vhdx size=536870912 log_size=1048576 block_size=0 subformat=fixed 3. qemu-img info lin.vhdx image: lin.vhdx file format: vhdx virtual size: 512M (536870912 bytes) disk size: 520M cluster_size: 8388608 4. Load lin.vhdx under Windows 10 is ok The same thing happens on `vpc` format with or without `oformat=fixed`, it seems that windows version of qemu-img has some incorrect operation? My guess is that windows version of qemu-img doesn't handle the description field of vpc/vhdx, which leads to an incorrect `disk size` field. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1759522/+subscriptions