qemu-nbd freezes access to VDI file

[Bump]

Mounted Oracle Virtualbox .vdi drive (dynamically allocated), which has GTP+BTRFS:
sudo modprobe nbd max_part=16
sudo qemu-nbd -c /dev/nbd0 /storage/btrfs.vdi
mount /dev/nbd0p1 /mydata/

Then I am operating on the btrfs filesystem and suddenly it freezes.

[John Snow (jnsnow)]

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?

[Bump (bump55)]

I thought there were qemu-img for that. Since qemu-nbd allows mounting images a rw block devices, it's logical to think that you can use it for that purpose. Will try to reproduce again the issue in case it was a kernel problem instead of qemu-nbd.

[John Snow (jnsnow)]

I agree, the program doesn't stop you from doing such things. It should work without error, but it might be slow. Just offering some advice you may not want to use it like this.

Try to reproduce with qcow2 and qemu-nbd to see if the problem is with our support of the disk image format or if it's a problem with e.g. the access patterns and qemu-nbd itself, for instance.

[Bump (bump55)]

Tied again with same .vdi as block device for 4 hours, didn't experience further problems. don't know how to reproduce the issue again, even don't know if has been fixed with any software update.

[Launchpad Janitor (janitor)]

[Expired for QEMU because there has been no activity for 60 days.]

[Launchpad Janitor (janitor)]

[Expired for btrfs-progs (Ubuntu) because there has been no activity for 60 days.]