Support for RAID in grub-setup

Support for RAID in grub-setup

[Jeroen Dekkers]

Hi all,

I'm a bit behind the schedule I created for SoC (I had some unplanned
things happening the last 2 weeks), but I've just committed the RAID
support for grub-setup and I'm going to work on LVM support very soon.

Grub-setup will ask Linux for the members of the RAID array that is
given as destination device. It will then install on the MBRs of those
devices and embed core.img after MBR. If it can't embed the core image
it will fail, I'm not sure whether we should support reading core.img
from a RAID array...

I let grub-setup put the RAID device directly into the prefix and put
-2 in grub_install_dos_part. I've modified make_install_device() in
init.c to leave the prefix alone when grub_install_dos_part is -2.

Jeroen Dekkers

Re: Support for RAID in grub-setup

[Yoshinori K. Okuji]

On Monday 24 July 2006 15:36, Jeroen Dekkers wrote:
> I'm a bit behind the schedule I created for SoC (I had some unplanned
> things happening the last 2 weeks), but I've just committed the RAID
> support for grub-setup and I'm going to work on LVM support very soon.

Great.

> Grub-setup will ask Linux for the members of the RAID array that is
> given as destination device. It will then install on the MBRs of those
> devices and embed core.img after MBR. If it can't embed the core image
> it will fail, I'm not sure whether we should support reading core.img
> from a RAID array...

Personally, I like to see that every part can be read from a RAID device, but 
maybe not so important in reality....

> I let grub-setup put the RAID device directly into the prefix and put
> -2 in grub_install_dos_part. I've modified make_install_device() in
> init.c to leave the prefix alone when grub_install_dos_part is -2.

So, if my understanding is correct, core.img is read from a single disk, but 
the rest is handled in a RAID device, right?

Okuji

Re: Support for RAID in grub-setup

[Jeroen Dekkers]

At Fri, 28 Jul 2006 00:20:42 +0200,
Yoshinori K. Okuji wrote:
> 
> On Monday 24 July 2006 15:36, Jeroen Dekkers wrote:
> > Grub-setup will ask Linux for the members of the RAID array that is
> > given as destination device. It will then install on the MBRs of those
> > devices and embed core.img after MBR. If it can't embed the core image
> > it will fail, I'm not sure whether we should support reading core.img
> > from a RAID array...
> 
> Personally, I like to see that every part can be read from a RAID device, but 
> maybe not so important in reality....

It would be possible to calculate how to write the image to the file
so it ends up being a consecutive image on the physical disk. But I
think it's not worth the trouble, especially given that we can always
embed the kernel if we keep the size below the 31k.

> > I let grub-setup put the RAID device directly into the prefix and put
> > -2 in grub_install_dos_part. I've modified make_install_device() in
> > init.c to leave the prefix alone when grub_install_dos_part is -2.
> 
> So, if my understanding is correct, core.img is read from a single disk, but 
> the rest is handled in a RAID device, right?

Yes, core.img is embedded after the MBR on the specific disk.  If you
can boot from a disk, it's a pretty safe to assume thatt you can also
read core.img for the same disk. Core.img includes the RAID module and
that is used to read everything else it needs.

Jeroen Dekkers

Re: Support for RAID in grub-setup

[Yoshinori K. Okuji]

On Friday 28 July 2006 01:13, Jeroen Dekkers wrote:
> It would be possible to calculate how to write the image to the file
> so it ends up being a consecutive image on the physical disk. But I
> think it's not worth the trouble, especially given that we can always
> embed the kernel if we keep the size below the 31k.

It would depend on the user... AFAIK, some stupid Windows software wants to 
use that region for something else.

> Yes, core.img is embedded after the MBR on the specific disk.  If you
> can boot from a disk, it's a pretty safe to assume thatt you can also
> read core.img for the same disk. Core.img includes the RAID module and
> that is used to read everything else it needs.

Nice!

Okuji

Re: Support for RAID in grub-setup

[Jeroen Dekkers]

At Sat, 29 Jul 2006 13:21:47 +0200,
Yoshinori K. Okuji wrote:
> 
> On Friday 28 July 2006 01:13, Jeroen Dekkers wrote:
> > It would be possible to calculate how to write the image to the file
> > so it ends up being a consecutive image on the physical disk. But I
> > think it's not worth the trouble, especially given that we can always
> > embed the kernel if we keep the size below the 31k.
> 
> It would depend on the user... AFAIK, some stupid Windows software wants to 
> use that region for something else.

I think the number of people who use RAID and such stupid Windows
software on the same hard disk is pretty small. :-)

This is probably different for LVM. But AFAIK we are currently always
overwriting the region and booting will fail if the stupid Windows
software overwrites that region.

Jeroen Dekkers