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From: Ivan Glushkov on 6 May 2008 15:40
Hi,

I installed Debian on top of LVM and software RAID1 following this:

http://dev.jerryweb.org/raid/


Everything is fine except that I cannot boot the Debian afterwards
("Insert boot disk" message from the bios). I used /dev/sdc and
/dev/sdd. First problem is that I do not know which hdd I should enter
as the first boot device in the bios. Moreover, obviously the bios does
not see the /dev/md0 array, since I guess first the raid array should be
started in order for grub to be loaded. I explicitly issued grub-install
/dev/md0 using the recovery mode of the debian installer, but that did
not help.

Thanks in advance,
Ivan


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From: Damon L. Chesser on 6 May 2008 22:50
Ivan,

My response probable did not make any sense. I went and dug up a blog
entry I made and reposted it. I covers the subject of how to make a
/boot on a software raid one. It does not cover the install, but rather
how to convert to a raid1 once you are up and running and how to install
grub onto both (or all) members of the array. www.damtek.com

HTH

--
Damon L. Chesser
damon(a)damtek.com
http://www.linkedin.com/in/dchesser


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From: Ivan Glushkov on 7 May 2008 13:40
Damon L. Chesser wrote:
> Ivan Glushkov wrote:
>> Hi,
>>
>> I installed Debian on top of LVM and software RAID1 following this:
>>
>> http://dev.jerryweb.org/raid/
>>
>>
>> Everything is fine except that I cannot boot the Debian afterwards
>> ("Insert boot disk" message from the bios). I used /dev/sdc and
>> /dev/sdd. First problem is that I do not know which hdd I should enter
>> as the first boot device in the bios. Moreover, obviously the bios does
>> not see the /dev/md0 array, since I guess first the raid array should be
>> started in order for grub to be loaded. I explicitly issued grub-install
>> /dev/md0 using the recovery mode of the debian installer, but that did
>> not help.
>>
>> Thanks in advance,
>> Ivan
>>
>>
>>
> Ivan,
>
> you can not put grub (/boot) on an LVM. You can put /boot on a raid1.
> If you made one raid1 device and made one partition on md0 you will not
> be able to boot (assuming you then put LVM on top of that one
> partition/used all of md0).

No, that's not the problem. I followed exactly the mentioned article.
There, two disks are used and partitioned in two partitions - the first
ones are used for one RAID1, which is formatted as ext3 and used for the
/boot directory (i.e. no lvm for /boot). The second partitions on both
disks are arranged in a second RAID1 array on which I have created
separate logical volumes for / /usr /var and so on.

>
> Redo what you did only make either two partitions to md0, one for boot
> (110Mb is large enough for most) and on partition2 put the rest of your
> system ontop of the LVM. Or, partition your two hds to have two mdadm
> raid1 . One small md0 for /boot and one md1 for the system with LVM on it.
>
> You will then have to install grub on to hdd or if hdc fails, you will
> not be able to boot as grub will be installed onto hdc MBR. Makes sense?

I taught I have to install the grub on the raid array, thus the grub
will put a copy of itself on the first partition on both hard drives,
used for the raid1, right?


>
> HTH
>




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From: Damon L. Chesser on 7 May 2008 14:00
snip
>
> I taught I have to install the grub on the raid array, thus the grub
> will put a copy of itself on the first partition on both hard drives,
> used for the raid1, right?
>

Wrong AFAIK. You can do that IF you have a boot loader on the MBR
pointing to grub. BIOS does not read software raid and knows nothing
about software raid. Software raid does not come into play until the
kernel via initrd is loaded. Install to the MBR of the first HD of the
array, then use grub to install into the MBR of the other members. If I
am wrong, then it is news to me, but hey, I will learn new things! See
my old "howto" on Linux, grub and raid at damtek.com for the exact
commands. It is not pretty, but it will work.

HTH

--
Damon L. Chesser
damon(a)damtek.com
http://www.linkedin.com/in/dchesser


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From: Ivan Glushkov on 7 May 2008 14:40
Damon L. Chesser wrote:
> snip
>>
>> I taught I have to install the grub on the raid array, thus the grub
>> will put a copy of itself on the first partition on both hard drives,
>> used for the raid1, right?
>>
>
> Wrong AFAIK. You can do that IF you have a boot loader on the MBR
> pointing to grub.

Now I am confused. Isn't grub a boot loader? Why would I need another
boot loader pointing to grub? I want to put grub on the MBR of both hard
drives from which my raid1 array consist of.

BIOS does not read software raid and knows nothing
> about software raid.

Indeed, but I do not expect from the bios to read my raid array. I
merely want it to look for boot record in the MBR of one of the two hard
drives on which I have my raid arrays.

Software raid does not come into play until the
> kernel via initrd is loaded. Install to the MBR of the first HD of the
> array, then use grub to install into the MBR of the other members.

What I meant with the paragraph you are referring to is exactly that:
issuing:

grub-install /dev/md0

should install (as fas as I understand it) a copy of grub in each hdd
from which the raid1 consist of (note: the partitions from both hard
drives included in md0 are both 512 MB and starting from the beginning
of the hard drives).

If I
> am wrong, then it is news to me, but hey, I will learn new things! See
> my old "howto" on Linux, grub and raid at damtek.com for the exact
> commands. It is not pretty, but it will work.

I tried that. Thanks.

Basically the problem was easily solved. I had to tag both partitions to
be used for my /boot raid1 array as primary and bootable (stupid of me,
I know). But there is now another problem:

I see already the grub initial screen, but when I hit enter, I get the
following:

Booting 'Debian GNU/Linux, kernel 2.6.24-1-amd64'

root (hd5,0)
Filesystem type unknown, partition type 0x7
kernel //vmlinuz-2.6.24-1-amd64 root=/dev/mapper/vg00-root ro linux26 quiet

Error 17: Cannot mount selected partition

Press any key to continue...

I suppose grub does not know anything about LVM and the partitions on
that. If I am right, I have to rebuild initrd, right? But how do I tell
it to enable the lvm?

Cheers,
Ivan


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