Am Mi., 17. März 2021 um 03:59 Uhr schrieb Chris Murphy
[off-list ref]:

On Tue, Mar 16, 2021 at 7:39 PM Qu Wenruo [off-list ref] wrote:

quoted

quoted

Using that restore I was able to restore approx. 7 TB of the
originally stored 22 TB under that directory.
Unfortunately nearly all the files are damaged. Small text files are
still OK. But every larger binary file is useless.
Is there any possibility to fix the filesystem in a way, that I get
the data less damaged?

 From the result, it looks like the on-disk data get (partially) wiped out.
I doubt if it's just simple controller failure, but more likely
something not really reaching disk or something more weird.

Hey Qu, thanks for the reply.

So it's not clear until further downthread that it's bcache in
writeback mode with an SSD that failed. And I've probably
underestimated the significance of how much data (in this case both
Btrfs metadata and user data) and for how long it can stay *only* on
the SSD with this policy.

Sorry Chris. I might have expressed this wrongly. But the
btrfs-filesystem was never on bcache. On bcache was a xfs-filesystem
that I backed up (rsynced) to the btrfs-filesystem when everything
went wrong. And I quickly gave up hope for that xfs afterwards, due to
the (lost) cached data of the directory-structure. That's why I'm
focusing on getting the backup on the btrfs-filesystem back.
But the possibility that some data is really wiped out or as Qu said,
that something is not reaching the disk gives me a direction to
investigate further. Maybe the raid-enclosure or the FC got damaged (I
ruled that out in the beginning). Eventually a failed raid-rebuild or
so. That would explain why so much data is missing.
Thank you.

Sebastian