Bug#491977: grub-probe fails with "Cannot find a GRUB drive for /dev/dm-N."

[Robert Millan]

severity 491977 important
thanks

On Mon, Jul 28, 2008 at 11:50:44PM +0200, Moritz Naumann wrote:
> > debby:~# cat /etc/mdadm/mdadm.conf 
> > DEVICE /dev/mapper/pdc_* 
> > DEVICE partitions
> > DEVICE /dev/sd*
> > DEVICE /dev/hd*
> > ARRAY /dev/md2 level=raid1 num-devices=1 spares=1 UUID=bc33d653:b8393c09:46829870:48df343b
> >    devices=/dev/sda6,/dev/sdb6
> > ARRAY /dev/md1 level=raid1 num-devices=1 spares=1 UUID=e8bd473c:ed7892ce:8a224776:594969e9
> >    devices=/dev/sda5,/dev/sdb5
> > ARRAY /dev/md0 level=raid1 num-devices=1 spares=1 UUID=b36bed37:7b1ca284:610ac217:8b54640c
> >    devices=/dev/sda1,/dev/sdb1
> > MAILADDR root
> > debby:~# 
> 
> 
> I do however have a FakeRAID-Controller on this system, It's a Promise
> initially set it up on the Boot PROM provided by this (sata_promise)
> FakeRAID.
> 
> debby:~# dmraid -r
> /dev/sdb: pdc, "pdc_jeedijde", stripe, ok, 320172928 sectors, data@ 0
> /dev/sda: pdc, "pdc_hbcdjbja", stripe, ok, 320172928 sectors, data@ 0
> debby:~#
> 
> Sorry for not explaining those configurations before, I sure did not
> mean to waste your precious time.
> 
> What I just did was to purge the mdadm package. After that, configuring
> the linux images just went fine, grub-probe works well and so does
> update-grub.
> 
> So basically we can blame this on my broken mdadm configuration?

I don't know enough about mdadm to determine whose fault is it.  But it seems
this is really a corner case problem, and only happens in a very specific
situation.  Therefore I'm lowering severity.

I'm CCing the mdadm maintainers;  maybe they know how could update-grub
reliably obtain the physical device names in your setup, or how to fix
mdadm so that it outputs physical devices in a way that makes update-grub
happy.

In any case, I wouldn't worry too much about this.  GRUB 2 introduces proper
RAID support, and then this is no longer a problem as it uses the same method
for installing on RAID than for loading stuff from a RAID during boot (and not
just RAID1 but also the non-trivial levels).

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."