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Re: howto boot from the second disk in raid 1



On Tue, Aug 23, 2011 at 5:21 PM, Bob Proulx <bob@proulx.com> wrote:
> Tom H wrote:
>> Bob Proulx wrote:


>>> For the new Grub2, I don't know. I haven't been able to learn it yet.
>>> Perhaps someone else will be kind enough to step up and say what needs
>>> to be done to install grub2 on a second disk. Probably just:
>>>
>>> grub-install /dev/sdb
>>
>> Correct.
>
> Oh good. Thanks for jumping in with information.

You're welcome.


>> And should work for grub1 too.
>
> But it doesn't work for grub1. I am hoping that it is improved with
> grub2 but don't know.

It works for grub1:

http://www.gnu.org/software/grub/manual/legacy/grub.html#Invoking-grub_002dinstall

And it also works with grub2 because it doesn't have a "grub" prompt
so there's no other way of populating "/boot/grub" and installing
grub2 to the MBR.


> I have tried grub-install /dev/sdb with grub1 and it does not create a
> bootable disk for me. I would need to set up a test case again to get
> to the details but what seems to happen is that doing that with grub1
> somehow creates a configuration where it only works if the disk is
> /dev/sdb. But if sda fails then on the reboot sdb rotates down to
> become sda and won't boot displaying an early part of the grub boot
> line but never getting to the grub boot menu. I remember once putting
> in another dummy disk just to hold the sda position to force the raid
> disk back to sdb and that enabled it to boot which caused me to
> believe somehow it is configured requiring it to be sdb and failing to
> work when it is sda. That problem is why it is necessary with grub1
> to specify the sdb device as (hd0) when issuing the grub setup
> command. Then it is configured as sda and in the future when it is
> sda it will boot.

Both of these work - and have worked for me. The first is the one that
most would agree is correct. As long as it works, I don't care.

#!/bin/sh
GRUB=/sbin/grub
$GRUB --batch --no-floppy <<EOF 1>/dev/null 2>/dev/null
device (hd0) /dev/sda
root (hd0,0)
setup (hd0)
device (hd1) /dev/sdb
root (hd1,0)
setup (hd1)
quit
EOF

#!/bin/sh
GRUB=/sbin/grub
$GRUB --batch --no-floppy <<EOF 1>/dev/null 2>/dev/null
device (hd0) /dev/sda
root (hd0,0)
setup (hd0)
device (hd0) /dev/sdb
root (hd0,0)
setup (hd0)
quit
EOF


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