How do md devices get assigned for initramfs load? [SOLVED]

John Klug · Last edited by John Klug on Fri Dec 18, 2009 7:29 am; edited 1 time in total

How does the system know during boot which /dev/sd? devices correspond to which md devices.

I have an md system that works, and am trying to make a 2nd one, but the 2nd one fails to load the devices.

Looking at my working system's initramfs file, /etc/mdadm.conf is not present. I would think it would be too late if it were in there anyway.

So how is the mapping done during boot assuming one uses genkernel? I used grub manually to specify root as follows:

root (hd0,0)
setup (hd0,0)
root (hd1,0)
setup (hd1,0)

Boot and initramfs are in the first disk and second disk in the first partition, which is ext2. Since the root menu works, It must be getting to the boot parition.

My non working system sees:

cassiol · Posted: Mon Dec 14, 2009 10:22 am Post subject:

helooo

this wiki help you with raid http://en.gentoo-wiki.com/wiki/RAID/Software

if you have more question, please post again
good luck
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please add [SOLVED] when your question is solved

John Klug · Posted: Wed Dec 16, 2009 5:30 am Post subject:

It looks like genkernel does not save /etc/mdadmin.conf. I suppose it could be added with an overlay to genkernel, but the above md line would be eaiser.

This answers my question, but I will open a new topic, since I now am closer to understanding my immediate problem (request_module: runaway ...), which lies with genkernel.

drescherjm · Posted: Wed Dec 16, 2009 5:40 am Post subject:

It normally does save /etc/mdadm.conf if you enable this in /etc/genkernel.conf
_________________
John

My gentoo overlay
Instructons for overlay

John Klug · Posted: Thu Dec 17, 2009 8:18 am Post subject:

So after putting in the /etc/mdadm.conf file in the initramfs file, it doesn't seem to do the assemble.

The boot complains about not finding real_root, and then I have to go into the shell and do:

mdadm --assemble

Then it creates my md devices.

Then I can continue the boot.

So how can I get mdadm to run automatically?

Is there any way to use the UUID number in /etc/mdadm.conf into the kernel line in grub.conf/menu.lst something like:

real_root=UUID=f7c6a4ab:69c4a123:120cd85d:8196c2c5

In my genkernel.conf I already have:

drescherjm · Posted: Thu Dec 17, 2009 4:33 pm Post subject:

I use these options on several machines here at work. All of my servers boot off of mdadm raid. I am not sure how many of them use the uuid syntax however. I know I do that at home. Do you have all the required drivers compiled into the kernel or are they modules? I have had issues when some parts were modules so I compile in raid456 and ext4/reiserfs.
_________________
John

My gentoo overlay
Instructons for overlay

drescherjm · Posted: Thu Dec 17, 2009 5:50 pm Post subject:

Here is one:

John Klug · Posted: Fri Dec 18, 2009 7:29 am Post subject:

I think the kernel doesn't seem to know about UUID for md.

Anyway, another one of my problems was that the disks came from another system (where I loaded them with gentoo), and one of the partitions got the wrong md number when the kernel booted, that did not match /etc/mtdamd.conf, because it was a rather high number. I tried to change /etc/fstab and /etc/mdadm.conf to match the kernel's version of the super-minor number, but then it wouldn't mount because mount said the partition was bad after the disk was assembled.

So I had to zero out the partition and re-create the md device number so that things wound up consistent. Apparently only --create can set the super-minor number.

So the super-minor numbers are essentially labels on the disks, so maybe you don't need the UUIDS. You just have to keep zeroing the superblocks to avoid minor number conflicts.

richard.scott · Posted: Mon Jan 04, 2010 12:56 pm Post subject:

Hi,

do you still get this output when booting:

John Klug · Posted: Tue Jan 05, 2010 3:55 am Post subject:

I wrote topic 807219. I didn't need to update cpio to fix my problem. Maybe I was just lucky?