Hi Duncan,
many many thanks for your nice explanation and pointing it out
what could happened.
> This reveals the problem. You have single chunks in addition
> to the raid1 chunks. Current btrfs will refuse to mount
> writable with a device missing in such a case, in ordered
> to prevent further damage.
> But meanwhile, while the above btrfs fi df reveals
> the problem as we see it on the existing filesystem,
> it says nothing about how it got that way. Your
> sequence above doesn't mention mounting the
> degraded raid1 writable once, for it to create those
> single-mode chunks that are now blocking writable
> mount, but that's one way it could have happened.
You're right, I booted first in to the installed system on the harddisk
and ended up in the rescueshell because obviously the "degraded" option
in the fstab is missing. So I mounted the harddisk manually with
the "degraded" option. But after that I decided to do the repairing
in a LiveSystem... I assume that is where the problem come from.
Because in the LiveSystem I wasn't able to mount the harddisk only
with the degraded option.
So as you mentioned either you fix the missing harddisk during the
running of the System or after that you have one shot (for example in
a LiveSystem), otherwise you have to copy from the readonly mounted
harddisk.
> Another way would be if the balance-conversion from
> single mode to raid1 never properly completed in the
> first place. But I'm assuming it did and that you
> had a full raid1 btrfs fi df report at one point.
> A third way would be if some other bug triggered
> btrfs to suddenly start writing single mode
> chunks. There were some bugs like that in the
> past, but they've been fixed for some time. But
> perhaps there are similar newer bugs, or perhaps
> you ran the filesystem on an old kernel with
> that bug.
Thank you and kind regards
Tamas Baumgartner-Kis
--
Tamás Baumgartner-Kis
Rechenzentrum der Universität Freiburg
Phone: +49 761 203 4605
E-Mail: Tamas.Baumgartner-Kis@xxxxxxxxxxxxxxxxxx
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