Re: One disc of 3-disc btrfs-raid5 failed - files only partially readable

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>> > Do you think there is still a chance to recover those files?
>>
>> You can use  btrfs restore  to get files off a damaged fs.
>
> This however does work - thank you!
> Now since I'm a bit short on disc space, can I remove the disc that
> previously disappeared (and thus doesn't have all the
> data) from the RAID, format it and run btrfs rescue on the degraded array,
> saving the rescued data to the now free disc?

In theory   btrfs restore   should be able to read files from
(unmounted) /dev/sdb (devid 2) + /dev/sdc (devid 3).
The kernel code should still be able to mount devid 2 + devid 3 in
degraded mode, but   btrfs restore  needs unmounted fs and I am not
sure if userspace tools can also decode raid5 degraded well enough.
For a single device, so non-raid profiles, it might be different.

lf you unplug /dev/sda (devid 1) you can dry-run  btrfs restore -v -D
<some_path>
and see if it would work.

If not, maybe first save the files that have csum errors with restore
(all 3 discs connected) to other storage and then delete the files
from the normally mounted 3 discs raid5 array and then do a normal
copy from degraded,ro mounted 2 disc to the newly formatted /dev/sda.
Hopefully there's enough space in total.
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