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

[Robert Millan]

On Thu, Jun 12, 2008 at 09:04:20AM +0200, Guido Günther wrote:
> On Wed, Jun 11, 2008 at 10:53:36PM +0200, Robert Millan wrote:
> > grub_util_get_grub_dev() returns the corresponding GRUB drive for a given
> > Linux device.  This can be (hdX), (mdX) or (some-lvm-name).
> Ah, o.k. that's why there's LVM names and hdX mixed - I see now. So if
> my device.map is:
> 
> (hd0) /dev/sda
> (hd1) /dev/sdb
> (hd2) /dev/mapper/mpath0
> 
> this should simply return (hd2)?

Yes, but ...

> > The question here is how GRUB should treat your multipath device.  If it
> > is like any normal device, in that the BIOS will report it to GRUB as a
> > disk, you should arrange grub_util_get_dev_abstraction() to return
> > GRUB_DEV_ABSTRACTION_NONE.
> 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.

> > 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?

-- 
Robert Millan

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<DRM> What good is a phone call… if you are unable to speak?
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