Comment 53 for bug 557429

> the minimum action required to fix the bug is to simply reject the
> second disk, updating its metadata in the process.
>
> > No, [updating metadata] really makes things worse! It prevents the
> > user/admin from managing arrays (parts in this case) by simply
> > plugging disks.
>
> No it does not.

Explain how it does not prevent to switch between conflicting changes by
hot-plugging.

> What it does is prevent the damage from growing worse
> without being noticed.

The real damage is prevented by mdadm, if mdadm --incremental returns
"mdadm: not re-adding /dev/... because it contains conflicting changes"
instead of setting up a corrupt array. Notice is also given by the
mdadm --monitor daemon reporting a "conflicting changes" event to
users/admins.

Being able to hot-plug/switch between conflicting changes is a
feature not a bug.

>
> > And what would be the gain of auto-removing writing metadate? If the
> > disks are connected during boot the disks will almost always stay in
> > the same order anyway, eliminating the gain to save that order
> > to metadata. If you want a specific order from the start, you need
> > to manually issue mdadm commands anyway. But now also if you need
> > another order than what was written to metadata. And all that mdadm
> > commands need to be issued in between an active hot-plugging
> > system (interference/no map file updating), instead of just
> > re-plugging your disks in order.
>
> As I already said, the gain is to prevent continued flip-flopping back
> and forth

What continued flip-flopping back and forth? Read again!

> between the two divergent filesystems based only on which
> disk is detected first. Almost always != always.

Almost always != always, because there are use-cases
where the user explicitly wants to hot-plug "flip-flop" several times
between the parts.

> You seem to be suggesting that the
> user physically disconnect one disk if they wish to access data on
> the other disk, rather than run mdadm.

Plugging disks is a nice and easy alternative these days.

Explain why it is a bad idea to plug and unplug (e)SATA disks plugged
into your laptop, or in your docking station, running an udev/mdadm
--incremental system.