On Wed, 08 Feb 2012 09:30:42 +0100 Stefan Priebe - Profihost AG
<s.priebe@profihost.ag> wrote:

> Hi Neil,
> 
> Am 08.02.2012 02:57, schrieb NeilBrown:
> > Probably mdmon isn't running for some reason.
> > 
> > For these arrays the metadata is managed in user-space by mdmon.
> > Until it is ready to record failures the array must remain readonly.
> > On of the first things it does is switch the array to read-write, having
> > arranged to catch any failure notifications.
> > 
> > If you 
> > 
> >  mdmon --all --takeover
> > 
> > it might just start working.  However that doesn't explain why mdmon wasn't
> > started at boot.  mdadm is meant to start it.
> > There are some concerns about mdmon starting this way being not "the right
> > thing" from a systemd perspective and there might be some issues there that
> > are causing problems.
> 
> You're correct the mdmon does not run as the root filesystem is readonly
> and it cannot create a pid file... and the root filesystem stays
> readonly as the mdmon is not running...

It should be configured to create it in a writable filesystem,
maybe /dev/.something or /var/run/something.

If it is configured to create it somewhere that isn't writeable when mdadm is
run, then that is a system integration error.

(not entirely surprising as we seem to keep changing our mind as to where
this stuff should go - I think /run is the flavour of the month).

NeilBrown