Bug#416512: removed disk && md-device

[Neil Brown]

On Wednesday May 9, bs at q-leap.de wrote:
> 
> Neil Brown <neilb at suse.de> [2007.04.02.0953 +0200]:
> >Hmmm... this is somewhat awkward.  You could argue that udev should be
> >taught to remove the device from the array before removing the device
> >from /dev.  But I'm not convinced that you always want to 'fail' the
> >device.   It is possible in this case that the array is quiescent and
> >you might like to shut it down without registering a device failure...
> 
> Hmm, the the kernel advised hotplug to remove the device from /dev, but you 
> don't want to remove it from md? Do you have an example for that case?

Until there is known to be an inconsistency among the devices in an
array, you don't want to record that there is.

Suppose I have two USB drives with a mounted but quiescent filesystem
on a raid1 across them.
I pull them both out, one after the other, to take them to my friends
place.

I plug them both in and find that the array is degraded, because as
soon as I unplugged on, the other was told that it was now the only
one. 
Not good.  Best to wait for an IO request that actually returns an
errors. 

> 
> >Maybe an mdadm command that will do that for a given device, or for
> >all components of a given array if the 'dev' link is 'broken', or even
> >for all devices for all array.
> 
> >   mdadm --fail-unplugged --scan
> >or
> >   mdadm --fail-unplugged /dev/md3
> 
> Ok, so one could run this as cron script. Neil, may I ask if you already 
> started to work on this? Since we have the problem on a customer system, we 
> should fix it ASAP, but at least within the next 2 or 3 weeks. If you didn't 
> start work on it yet, I will do...

No, I haven't, but it is getting near the top of my list.
If you want a script that does this automatically for every array,
something like:

  for a in /sys/block/md*/md/dev-*
  do
    if [ -f $a/block/dev ]
    then : still there
    else
	echo faulty > $a/state
	echo remove > $a/state
    fi
  done

should do what you want. (I haven't tested it though).

NeilBrown