Re: btrfs suddenly think's it's raid6

[marble <marble@hamburg.ccc.de>]

> No log_root* in the super. So no fsyncing at the time? What was
> happening at the time of the power loss?
That I don't know.

> Pretty weird, all three supers are OK and yet two copies of the fs
> tree are corrupt. Why doesn't it fall back automatically to one of the
> other roots?
> 
> You could try 'mount -o usebackuproot,ro' and see if that's permissive
> enough to succeed.
That yields the same result
```
marble@archlinux ~ % sudo mount -o usebackuproot,ro /dev/mapper/black
/tmp/black
mount: /tmp/black: can't read superblock on /dev/mapper/black.
```
> I wonder if the drive firmware reordered things contrary to Btrfs
> expectation right at the powerfail - or even if the powerfail caused
> the drive firmware to do the writes in the wrong order?
> 
>