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

[Guido Günther]

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)?

> 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.

> 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).

> And if it's something fancier like RAID or LVM, it'll take some work to
> implement.
Looking at the LVM code that's probably not necessary. I'll have another
stab at the code when I'm near some test hardware again next week.
Cheers,
 -- Guido