Booting from Raid1 (/ and /boot on the same system) [solved]

Sedrik · Last edited by Sedrik on Sat Dec 27, 2014 2:50 pm; edited 1 time in total

Hi all

This is my setup.

/dev/md0 100G rootfs (contains / and /boot) Raid1

Grub seems to not find the files on disk as all I get is the grub prompt when booting.

I have installed grub on three of the disks (the fourth one complains about multiple labels and refuses to install grub)

I have tried to point my grub.conf to run the rootfs on both /dev/md0 and /dev/sda1 to no success.

I'm sorry if this is short but I am writing from my laptop and don't have a easy way of transfering the config files to it for you all to investigate.

What steps is needed to make this work? Do I need a custom initramfs to boot from /dev/md0?
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lagalopex · Guru Joined: 16 Oct 2004 Posts: 562

What filesystem is your / (containing the /boot)?
Raid1 over four disks, nothing else?
MBR or GPT partitioned disks?
"grub legacy" (0.97) or "grub 2"?
"grub promt"... what exact error message? grub loads but it does not find any kernels? have you tried to find the kernels? (perhaps wrong "path"?)

initrd is not necessary as long as your kernel directly includes the needed parts (eg. sata controller, mdraid and filesystem).

NeddySeagoon · Posted: Sat Dec 27, 2014 11:24 am Post subject:

Sedrik,

Which version of grub are you using and which version of raid metadata?

With grub2 the raid metadata version does not matter but you need to assemble the raid set before root can be mounted.
grub has no make its own arrangements for finding and reading /boot.

With legacy grub, the raid set where /boot is must be Version : 0.90.00 raid metadata.

Sedrik · Posted: Sat Dec 27, 2014 1:32 pm Post subject:

Metadata version is 0.90.00

I use grub 2.02_beta2-r3

/ is a ext4 filesystem

It's 4 primary partitions running Raid1 and 4 primary ones running a Raid5 system (1 of them is a spare). (/dev/md0 is sd[abcd]1 and /dev/md1 is sd[abcd]2)

The error I get when trying to install grub on sdd is
"warning: Attempting to install GRUB to a disk with multiple partition labels. This is not supported yet..
error: embedding is not possible, but this is required for RAID and LVM install."

I get no error when I try to boot the machine from disk only the grub> prompt where it tells me I need to load the kernel before booting (if I try the boot command).

Thanks for all the help.
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From Gentoo with love

NeddySeagoon · Posted: Sat Dec 27, 2014 1:41 pm Post subject:

Sedrik,

Lets ignore the sdd issue for now. The grub> prompt means that grub cannot find its configuration file. In this case grub.cfg.

Your original post says

Sedrik · Posted: Sat Dec 27, 2014 2:09 pm Post subject:

Ah, that was something I had completely missed =)

Now it boots but it did not remount / to the raid (rather booted into one of the discs) How can I fix that?
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Sedrik · Posted: Sat Dec 27, 2014 2:49 pm Post subject:

Ok, seems to be me just forgetting to update fstab.

Now everything seems to be working as I want it too =)

Many thanks for all your help!
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From Gentoo with love

NeddySeagoon · Posted: Sat Dec 27, 2014 2:50 pm Post subject:

Sedrik,

Your raid will now be out of sync.

I guess you have root=/dev/sda in grub.cfg ?
You need root=/dev/md...

Why do you say it booted to one of the discs?
If that is really what happened, the next and subsequent attempts to assemble the raid will either fail or result in the raid running in degraded mode.
You will need to add the missing element back into the raid set, so it can sync again.

/proc/mdstat will tell you what is going on. I get

Sedrik · Posted: Sat Dec 27, 2014 3:29 pm Post subject:

It seems to be all fine

NeddySeagoon · Posted: Sat Dec 27, 2014 3:37 pm Post subject:

Sedrik,

Looks good. Raid5 either works or it doesn't. There is no possibility of it starting on only one disk.
It can and will start on n-1 disks though.

Thats why you run the monitor, so it emails you about nasty things happening to your raid set that don't actually stop it working.
You can still get unlucky. I had two drives kicked out of a raid5 set only 15 minutes apart.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Sedrik · Posted: Sat Dec 27, 2014 11:06 pm Post subject:

Yeah thats why I am running a Spare in it now (ran 4 disks without a spare before this change).

Hopefully I will be able to keep all my data. Will look for a good way of doing of-site backups of the most precious stuff though (images and what not)
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From Gentoo with love

steveL · Posted: Tue Jan 06, 2015 1:54 pm Post subject:

@Sedrik: Can I ask what your fstab looks like? It would be useful for others searching this forum in future.

Thanks,
steveL.