I've been backing up physical Windows disks from a Linux bootable USB by converting the raw drive directly into a dynamically expanding VHDX file with qemu-img. The images are stored on a TrueNAS SMB share, and the process looks like this: qemu-img convert -f raw -O vhdx -o subformat=dynamic -p /dev/nvme0n1 /mnt/backupdir/machine-name.vhdx. The main advantages are that the image can be mounted and accessed from Windows, booted as a Hyper-V virtual machine, or converted back to a raw disk. If I boot the image in Hyper-V, I remove unknown devices with PowerShell and pnputil. The dynamic image also uses less storage than a full raw-disk copy while preserving the original partition sizes. Are there any drawbacks or reliability concerns with using VHDX files this way instead of a dedicated backup product?
3 Answers
A major benefit is the recovery flexibility: Windows can mount the file, Hyper-V can use it as a virtual disk, and it can be converted back to a physical-disk image. The dynamic format generally saves space compared with copying every sector of the disk, while the virtual disk’s partition layout remains the same. The tradeoff is that you’re building and maintaining the backup process yourself rather than using a mature product with built-in restore-to-different-hardware and instant-recovery features.
The images can be created from a Linux boot USB and written directly to an SMB share. After mounting the share with cifs-utils, tools such as lsblk can identify the source disk and qemu-img can create the VHDX. That makes this a practical no-license-cost workflow, provided the storage and network connection are reliable.
The approach is workable, especially if the flexibility of mounting the image or running it in Hyper-V is important. Just make sure the source is captured in a consistent state and regularly test both mounting and restoring the image to another disk or VM. A raw conversion is essentially a disk image, so it won’t automatically provide the versioning, verification, application-aware backups, or scheduling that a dedicated backup system might offer.
That flexibility is exactly why I prefer it. Windows’ built-in backup tools also use VHDX, but this gives me a straightforward way to capture the entire disk and keep the images on my own storage without licensing costs.