On Tue, Mar 23, 2021 at 12:50 AM Dave T [off-list ref] wrote:

quoted

d. Just skip the testing and try usebackuproot with a read-write
mount. It might make things worse, but at least it's fast to test. If
it messes things up, you'll have to recreate this backup from scratch.

I took this approach. My command was simply:

    mount -o usebackuproot /dev/mapper/xzy /backup

It appears to have succeeded because it mounted without errors. I
completed a new incremental backup (with btrbk) and it finished
without errors.
I'll be pleased if my backup history is preserved, as appears to be the case.

I will run some checks on those backup subvolumes tomorrow. Are there
specific checks you would recommend?

It will have replaced all the root nodes and super blocks within a
minute, or immediately upon umount. So you can just do a 'btrfs check'
and see if that comes up clean now. It's basically a kind of rollback
and if it worked, there will be no inconsistencies found by btrfs
check.



-- 
Chris Murphy