I don't recommend you use VDI images in this way; we do not intend to support performant RW access; support for VDI images is there to convert to qcow2 or raw, generally.
That said, some questions that might be interesting to know the answer to:
- Try converting your VDI image to raw or qcow2 and mounting that instead. Does the conversion work successfully? Can you export that image via qemu-nbd and mount it? Does it work?
- Do non-BTRFS filesystems cause any problems?
I don't recommend you use VDI images in this way; we do not intend to support performant RW access; support for VDI images is there to convert to qcow2 or raw, generally.
That said, some questions that might be interesting to know the answer to:
- Try converting your VDI image to raw or qcow2 and mounting that instead. Does the conversion work successfully? Can you export that image via qemu-nbd and mount it? Does it work?
- Do non-BTRFS filesystems cause any problems?