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ebnerjoh
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PostPosted: Tue Apr 03, 2012 6:00 pm    Post subject: Raid + LVM: Problems with grub Reply with quote

Hello!

I used the "RAID + LVM" Doku on www.gentoo.org to install a new gentoo system on 2 hard disks. The issue is, I have only one hdd available at the momen.

I created 2 Raid1:

/dev/md1 and /dev/md3 with "mdadm --create /dev/mdX --level=1 --raid-devices=2 /dev/sdaX missing"

Then I created one volume-group and one logical volume "root" which I am using as root-Partition.

Then I created a ext2 filesystem on /dev/md1 and a ext4 filesystem on /dev/vg/root.

Everything is fine, except grub. I was not able to execute root (hd0,0), the errormessage was "unknown filesystem".

Then I tried to install grub2. But when executing "grub-install" I am getting the errormessage "/usr/sbin/grub2-probe: warning: Couldn't find physical volume '(null)'. Some modules may be missing from core image.."

What is going wrong?

Br,
Johannes
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vrghost
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PostPosted: Thu Apr 05, 2012 10:45 am    Post subject: Reply with quote

I might be wrong, but it sounds like you are using md1 as boot and md3 as root (or some such combination)
The problem in that case is that root(0,0) is pointing to the underlying device (dev/sda1), which contains half of a raid device, and not a file system, to access the filesystem you need to access /dev/md0, uncertain if grub (or the initial kernel) can do that. Even if you ad domdadm to the line.

Suggest you create a small boot partition, then you can try to set the root partition to /dev/md3, know that when you do a similar trick with lvm it is suggested that you also put root (/) on a normal system, then mount /usr /opt /var and /home on lvm drives, but think you might be able to get only /boot on a normal fs as the kernel SHOULD (I may be wrong) have the drivers and mdadm loaded by the time it builds the root file system (you will also need to use initramfs)
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ebnerjoh
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PostPosted: Thu Apr 05, 2012 11:09 am    Post subject: Reply with quote

vrghost wrote:
I might be wrong, but it sounds like you are using md1 as boot and md3 as root (or some such combination)
The problem in that case is that root(0,0) is pointing to the underlying device (dev/sda1), which contains half of a raid device, and not a file system, to access the filesystem you need to access /dev/md0, uncertain if grub (or the initial kernel) can do that. Even if you ad domdadm to the line.


Yes, exactly:
/dev/md1 is the boot partition (sda1 and in future sdb1)
/dev/md3 is the root partition (sda3 and in future sdb3)

I didn't understand you correctly. You think it is not possible at all (I am running the same config on a old PC) or just because of the missing sdb?

My problem is, that the second HDD (future sdb) is still running on the productive system...

Br,
Johannes

BTW: I am following the doku http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml but not using LVM anymore and using "mdadm .... /dev/sdaX missing"
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ebnerjoh
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PostPosted: Fri Apr 06, 2012 5:20 am    Post subject: Reply with quote

I have an idea... Maybe it is because of Metadata 1.2 when creating the raid drives. I am now reinstalling the system with metadata 0.9.

Let's see...

Br,
Johannes
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ebnerjoh
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PostPosted: Fri Apr 06, 2012 9:38 am    Post subject: Reply with quote

I can confirm that the metadata was the issue. Changing from 1.2 to 0.9 fixed my grub problem.

Br,
Johannes
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