Filesystem unmountable

Good day,

This might be something you are already aware of, but I thought I should
inform someone of what happened to my sytem.

I was running ArchLinux with kernel 4.1.3-1-ARCH #1 SMP PREEMPT x86_64
GNU/Linux and executed btrfs-convert /mnt from an ArchLinux live disk to
convert my ext4 filesystem to btrfs.

The conversion was seemingly successful, but after booting journalctl
--verify reported some corrupt files. I saw on a an online post that I
should try to do a btrfs balance start after converting from ext4, and so I
executed the command and left the laptop to complete the task. The next
morning however I found the system frozen and had to do a hard reset. After
this the filesystem was unmountable.

The initial boot after the hard reset left me in an emergency shell at
which point I tried to mount the system and the shell stopped responding.
Booting a live disk and running btrfsck exited with a segmentation fault.
Attempts to mount the filesystem also exited with a segmentation fault or
the shell seemed to be waiting for the command to complete for very long
and did not respond to CTRL-C.

I know nothing of kernels or filesystem drivers and I hope I am not
waisting any body's time with something that was probably my own fault. I
have since reinstalled my OS and in hindsight I should probably have
attempted to save some of the kernel log files.

Kind regards,
Neels van Rooyen

There appears to be some regressions in btrfs-convert that are in the
list archive over the last month in particular - but I think the
problems particularly started to surface about 6ish months ago. When I
filed the bugs I was seeing with converted ext4 file systems, they
were completely consistently reproducible. But then I went back a few
days later to the same source qcow2 that I was snapshotting (qcow2
snapshot, not a btrfs snapshot) to do the testing, and the problem did
not always trigger. But fortunately Qu has reproduced this and is
working on it.

In your case it might be possible to mount with ro,recovery and get
data off of it. Or you might have to resort to btrfs restore if it's
badly broken and at least get /home data out of it.  If you have
backups, it's easier to just obliterate it and start over, unless you
want to experiment and learn more with btrfs restore...


Chris Murphy