there's a bug in 6.7 with filesystems that are mid upgrade and then get downgraded not getting marked in the superblock as downgraded, and this translates to a really horrific bug in splitbrain detection when the old version isn't updating member sequence nmubers and you go back to the new version - this results in every device being kicked out of the fs.
and our backports are not being picked up by the stable team, so - do not run 6.7, switch to 6.8 immediately, running 6.7 with new -tools will trigger it. if you are affected: - 6.9 (once Linus merges) will have a new no_splitbrain_check option, which runs the splitbrain checks in dry mode and won't kick your devices out - we have new repair code landing soon that can recover from missing/unreadable btree roots by scanning the entire device(s) for btree nodes (which, fortunately, we have sufficient metadata in btree node headers to do safely; reiserfs famously did not). i've seen some crazy corruption resulting from this, but it might still be recoverable
