Unable to install bootloader on software raid

[Johann Spies]

After two of my hard disks failed, I decided to use a software raid in future and tried to install Debian Testing on the raid.  The configuration of the raid and software installation went well until I tried to install the bootloader.  Both Grub and Lilo refused to install.

If it is not possible to install Grub or Lilo onto a software raid, why is the option available in Grub?

I have seen several efforts to solve this problem on the internet, but none of them worked for me.

What is the way to install Debian onto a software raid?

Regards
Johann

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Because experiencing your loyal love is better than life itself,
my lips will praise you.  (Psalm 63:3)

[Renaud OLGIATI]

On Sat, 13 Dec 2014 11:36:58 +0200
Johann Spies <johann...@gmail.com> wrote:

> What is the way to install Debian onto a software raid?

I have installed 7.7.0-64 from the DVD without any problem.

So it might be something in Testing ?

Did you try to install from a Live-CD/DVD ? ISTR that in that case you must add dmraid=true at the end of the GRUB boot line.

Cheers,

Ron.
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[Johann Spies]

Thanks for your reply, Ron.

In the end I configured my partions to exclude the first 250Mb (/boot) from the raid and I could install Grub just to have a working system.

It is not the best solution.  The installer should work as expected.

[Pascal Hambourg]

Johann Spies a écrit :

>
> In the end I configured my partions to exclude the first 250Mb (/boot) from
> the raid and I could install Grub just to have a working system.
>
> It is not the best solution.

Obviously it's not. /boot should be on a RAID (and the bootloader
installed on all disks, which the installer won't do automatically) in
order for the system to be able to boot after any disk failure.

How did you prepare the disks the first time ?

PS : dm-raid is needed only if you want to use software BIOS RAID (aka
fakeRAID, not recommended), not Linux native RAID.

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[Darac Marjal]

On Sat, Dec 13, 2014 at 11:36:58AM +0200, Johann Spies wrote:
> After two of my hard disks failed, I decided to use a software raid in
> future and tried to install Debian Testing on the raid.  The configuration
> of the raid and software installation went well until I tried to install
> the bootloader.  Both Grub and Lilo refused to install.
>
> If it is not possible to install Grub or Lilo onto a software raid, why is
> the option available in Grub?
>
> I have seen several efforts to solve this problem on the internet, but
> none of them worked for me.
>
> What is the way to install Debian onto a software raid?

I think the problem is that, depending on the RAID level, the BIOS won't
be able to read the disks in order to load GRUB. If you're running
RAID0, then you're in luck; both drives appear as normal disks and all
that RAID does is ensure they are kept identical. If you're running
RAID1, though, then each disk is a chopped-up mess of data and you NEED
the RAID to provide the hint that half the data is on another device.

Now, once grub is loaded, it CAN assemble the RAID to a sufficient point
to load all the pieces of the kernel, but if the BIOS can't make enough
sense out of the disk to load GRUB then you have a problem. In that
case, you would normally leave a portion of the disk unRAIDed and
install GRUB onto that.

[Sven Hartge]

Darac Marjal <maili...@darac.org.uk> wrote:

> I think the problem is that, depending on the RAID level, the BIOS won't
> be able to read the disks in order to load GRUB. If you're running
> RAID0, then you're in luck; both drives appear as normal disks and all
> that RAID does is ensure they are kept identical. If you're running
> RAID1, though, then each disk is a chopped-up mess of data and you NEED
> the RAID to provide the hint that half the data is on another device.

It's the other way round: RAID0 is striped, aka "chopped up mess" and
RAID1 are mirrored disks.

S°

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[Pascal Hambourg]

Sven Hartge a écrit :

> Darac Marjal <maili...@darac.org.uk> wrote:
>
>> I think the problem is that, depending on the RAID level, the BIOS won't
>> be able to read the disks in order to load GRUB. If you're running
>> RAID0, then you're in luck; both drives appear as normal disks and all
>> that RAID does is ensure they are kept identical. If you're running
>> RAID1, though, then each disk is a chopped-up mess of data and you NEED
>> the RAID to provide the hint that half the data is on another device.
>
> It's the other way round: RAID0 is striped, aka "chopped up mess" and
> RAID1 are mirrored disks.

Besides, the Linux RAID arrays usually do no reside on whole raw disks
but on RAID partitions. GRUB's boot image and core image are usually
installed on each disk outside these partitions. This way all the
sectors needed to load GRUB's core image can be found on each single
disk, regardless of the RAID level.

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