Bug#483971: Fwd: Re: grub-installer: no support for dmraid and multipath for grub2

[Guido Günther]

On Mon, Jun 16, 2008 at 10:56:06PM +0200, Robert Millan wrote:
> > No. The bios doesn't now anything about the multipathing. It sees a
> > number of identical scsi devices sda[a-d] while Linux multipaths this to
> > /dev/mapper/mpath0.
> 
> ... then /dev/mapper/mpath0 doesn't belong in device.map.
O.k. So the device map only lists Bios/EFI devices?

> > > If it's just an alias for an existing device, we'll probably have to
> > > think this through.
> > /dev/mapper/mpath0 is kind of an alias for the underlying paths (e.g.
> > /dev/sda[a-d]). So whenever grub wants to access /dev/sd? it should
> > access the /dev/mapper/mpathX instead. Does this qualify as an alias?
> > There are two ways to find out which /dev/sd? build up the multipath
> > device: Looking at the multipath -l output or looking at the dm map
> > (like I've implemented it in parted).
> 
> So how is this different from software RAID-1?
I think it doesn't differ that much - this is why we could reuse most of
the grub-installer code for grub1. The basic poinst is that we need grub
to write the MBR onto /dev/mapper/mpathX and that the partitions are
/dev/mapper/mapthX-partY instead of /dev/sdaY. 
This is a bit of a special case but sufficient for the installer.
 -- Guido
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