Re: 5.6 pretty massive unexplained btrfs corruption: parent transid verify failed + open_ctree failed

[Roman Mamedov <rm@romanrm.net>]

On Wed, 12 Aug 2020 15:34:33 -0700
Marc MERLIN <marc@merlins.org> wrote:

> Because it's an external array, I do stop it to save power and do this:
> umount /dev/mapper/crypt_bcache0
> sync
> dmsetup remove crypt_bcache0
> echo 1 > /sys/block/md6/bcache/stop
> mdadm --stop /dev/md6
> /etc/init.d/smartmontools stop
> sleep 5
> pdu disk3 off  <= cuts power
> 
> Note that I umount, then sync just in case, then a bunch of stuff to
> free up block devices, but by then the btrfs FS has been unmounted and
> synced.

Or should have been. If it's a copy-paste from a shell script (unless you do
the whole process manually every time), it doesn't appear like you check the
success status of each line before continuing to the next. Either add
"|| exit 1" to each of these that can fail, or just use "#!/bin/bash -e" in
the script's first line.

As is, imagine umount fails ("target busy"), then dmsetup fails ("device in
use"), then mdadm fails to stop the array, but then you cut power to the
entire thing anyways.

-- 
With respect,
Roman