Re: "kernel BUG" and segmentation fault with "device delete"

[Chris Murphy <lists@colorremedies.com>]

On Fri, Jul 5, 2019 at 3:48 PM Chris Murphy <lists@colorremedies.com> wrote:
>
> We need to see a list of commands issued in order, along with the
> physical connected state of each drive. I thought I understood what
> you did from the previous email, but this paragraph contradicts my
> understanding, especially when you say "correct approach would be
> first to convert all RAID 10 to RAID1 and then remove devices but that
> wasn't an option"
>
> OK so what did you do, in order, each command, interleaving the
> physical device removals.


To put a really fine point on this, in my estimation the data on sdf
and sdd are hanging by a thread. It's likely you have partial data
loss because clearly some Btrfs metadata is missing and there are no
other copies of it. For sure you do not want to try to repair the file
system, or do anything that will cause any writes to happen. Any
changes to the file system now will almost certainly make problems
worse, and the chance of recovery will be reduced.

#1: Reconnect the last missing device. Obviously Btrfs wants it
because there's necessary metadata on that drive that doesn't exist on
sdf or sdd.
#2: Only mount the volume ro from here on out. Even a rw mount might
make things worse.
#3: Rsync copy everything you care about off this volume onto a new
volume. At some point this rsync will fail when Btrfs discovers the
missing metadata, which is why you really need to follow step #1. But
if that missing drive is already wiped and retasked for some other
purpose, you're looking at a data recovery operation. Not a file
system repair operation.

Your best chance to avoid total data loss is to get as much off the
volume as you can while you still can. And then after that see if you
can get more off of it - which I think is doubtful.


-- 
Chris Murphy