I've been using qemu-img from a Linux bootable USB to convert complete raw Windows disks into dynamically expanding VHDX files stored on a TrueNAS SMB share. The command is: qemu-img convert -f raw -O vhdx -o subformat=dynamic -p /dev/nvme0n1 /mnt/backupdir/machine-name.vhdx. The advantage is that the image can be mounted in Windows, attached to Hyper-V for instant recovery, or converted back to a raw disk. If I boot the image in Hyper-V, I remove unknown devices with PowerShell using Get-PnpDevice and pnputil. The dynamic image also uses less space than a full raw-disk copy while preserving the original partition sizes, and there are no licensing costs. Are there any reliability, consistency, or recovery concerns with using VHDX files this way, or is this a reasonable backup practice?
3 Answers
The workflow is practical for creating a portable disk image. Boot a Linux environment, install qemu-utils and the SMB tools, mount the network share, identify the source disk with lsblk, and convert it to VHDX. Just make sure the image is created from a quiescent or offline system so files are not changing during the copy, and regularly test mounting or booting the result. A backup that has never been restored is only an assumption.
VHDX is a useful format for this because Windows and Hyper-V can work with it directly, and dynamic allocation can reduce the amount of storage consumed. However, the file itself is not a complete backup strategy: keep multiple versions, protect the files from accidental deletion or ransomware, verify their checksums, and maintain at least one separate copy. Also confirm that your restore process works with different hardware, since drivers and boot configuration can still prevent a restored Windows installation from starting.
There are commercial and built-in backup tools that already support dissimilar-hardware recovery and instant recovery, so it may be worth comparing their consistency checks, incremental backups, scheduling, and bare-metal restore features. That said, your approach can be perfectly reasonable when you specifically want an uncomplicated, license-free image that can be attached to Windows or Hyper-V. The main limitation is that a raw conversion is essentially a disk clone, not an application-aware backup with automatic versioning or transactional handling.
That portability is the main reason I prefer it. I can mount the image on another Windows system, attach it to the native hypervisor, or convert it back to a raw disk when needed. I’m also keeping the images on a separate network storage system rather than only on the source machine.