>> All would be clearer if * mdadm -E would report "missing" instead of
>> removed (which sounds like it really got "mdadm --removed")
>
> There already exists a faulty state. It might be appropriate to use that

This and the detection process sounds reasonable to me.


I am not sure how much sense auto-removing a confilicting part from an array 
makes from the user side. As the order in which devices appear can be random or 
not, I would rather like mdadm to refrain from doing any metadata updates based 
on that, if it is not necessary.

With mdadm patched to detect and report conflicting changes and not to
sync conflicting changes without --force, it should protect from unaware
data-loss and corruption and always provide a coherent state, consisting
of the first or (maybe intentionally even) only part that appears from
an array.

A coherent mdadm way of informing the user about the appearance of
conflicting changes (after a run degraded event) to  would probably be
to emit a  "conflicting changes" mdadm --monitor event.

If mdadm --incremental would auto-remove a part with confilicting
changes, it might not remove the correct part the user may actually
--remove. But the situation would look very similar as if some admin had
actually --removed something. Possibly wrongly suggesting to the admin
that its a simple and safe matter of re-adding, while he actually needs
to manually reverse the auto-remove operation, to prevent critical data-
loss.

-- 
array with conflicting changes is assembled with data corruption/silent loss
https://bugs.launchpad.net/bugs/557429
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