On Tue, Aug 9, 2011 at 6:31 PM, NeilBrown [off-list ref] wrote:

It need /proc, /sys, and /dev (assuming udev).
There is really no point in unmounting any of these as they are virtual.
Unmount everything else, remount root readonly, then "mdadm --wait-clean".

However I would expect missing filesystems to cause an early failure rather
than a hang.  If mdmon had been killed already that might cause a bit of a
hang, but it should be limited to 5 seconds.

Maybe run 'mdadm --wait-clean --scan' under 'strace' and see what it is
doing??

NeilBrown

I actually forgot I posted to this list so long ago. I hesitated about
posting here and resurrecting it, but I figured it'd be for the
benefit of others searching about this problem with gentoo.

I eventually traced the problem to a script while shutting down, it
killed all running processes (including mdmon.) I had an almost
working solution, and with a collaboration with someone else on the
gentoo forums, there's a full solution now.

The forum thread is @
http://forums.gentoo.org/viewtopic-t-888520.html

I've reported it as a bug on the bugtracker, I've also got a
workaround for it on that bug report:
https://bugs.gentoo.org/show_bug.cgi?id=395203

The workaround still hasn't made it into the main repository.

Hopefully this will get threaded properly...