Linux raid wiki - force assembling an array where one drive has a different event count - advice needed

[Wols Lists <antlists@youngman.org.uk>]

As I understand it, the event count on all devices in an array should be
the same. If they're a little bit different it doesn't matter too much.
My question is how much does it matter?

Let's say I've got a raid-5 and suddenly realise that one of the drives
has failed and been kicked from the array. What happens if I force a
reassemble? Or do a --re-add?

I don't actually have a clue, and if I'm updating the wiki I need to
know. What I would HOPE happens, is that the raid code fires off an
integrity scan, reading each stripe, and updating the re-added drive if
it's out-of-date. Is this what the bitmap enables? So the raid code can
work out what changes have been made since the drive has been booted?

Or does forced re-adding risk damaging the data because the raid code
can't tell what is out-of-date and what is current on the re-added drive?

Basically, what I'm trying to get at, is that if there's one disk
missing in a raid5, is a user better off just adding a new drive and
rebuilding the array (risking a failure in another drive), or are they
better off trying to add the failed drive back in, and then doing a
--replace.

And I guess the same logic applies with raid6.

Cheers,
Wol