Apologies, I missed the required commands, output from them is as
follows & attached.

$ uname -a
Linux data-acorn-token 5.12.5-arch1-1 #1 SMP PREEMPT Wed, 19 May 2021
10:32:40 +0000 x86_64 GNU/Linux
$ btrfs --version
btrfs-progs v5.12.1
$ sudo btrfs fi show
Label: 'Parallel eXceed'  uuid: 2d80eaf7-6588-41b3-add3-1d4a3a2996eb
        Total devices 2 FS bytes used 281.77GiB
        devid    1 size 317.71GiB used 317.71GiB path /dev/nvme0n1p6
        *** Some devices missing
# Can't show btrfs fi df, I don't want to mount it!
$ sudo dmesg >dmesg.log # attached to email

On Wed, May 19, 2021 at 11:45 PM Octavia Togami
[off-list ref] wrote:

Hi,

I recently was trying to expand my root drive while booted into it, so
I made a new partition and did `btrfs device add /dev/the-partition
/`, then `btrfs balance start -dconvert=raid0 -mconvert=raid1 /`. It
segfaulted, and I determined it would be easier for me to just boot
into a live CD and move/resize it there; but when gparted attempted to
do the operation it failed `btrfs check`. I updated all my packages,
and then re-ran `btrfs check` and the output is attached. Is there a
fix?