View Full Version : [xubuntu] raid / grub configuration issue

April 26th, 2009, 05:50 PM
With reference to this earlier post re: my raid / lvm configuration (http://ubuntuforums.org/showpost.php?p=7134682&postcount=4) and eventual installation...

...I am trying to resolve what seems to be a grub-related wrinkle:

a. I have discovered that the system does not boot from the bootable md0 array, consisting of...

sda1 - RAID1 - (md0) - ext3 - /boot (500mb)
sdb1 - RAID1 - (md0) - ext3 - /boot (500mb)
b. The system boots, instead, from the "plain vanilla" (non-RAID and non-LVM) sdc1 partition...

sdc1 - ext3 - /boot (500mb)
c. grub> find /grub/stage1 indicates...

d. /dev/sdc1 does show up in fstab with /boot as it's mount point.

e. /dev/md0 (the bootable RAID1 array) does not show up in fstab.

All else seems to be in good order:

f. The md0 array shows up as it should when I run mdadm diagnostics.

g. fdisk -l shows all partitions (sda1, sdb1, sdc1) configured as bootable ("*").


1. How can I make the md0 array bootable (as I had originally intended) and what do I need to do with regard to grub and fstab to fix the wrinkle?

2. Could it be that when the partition tables were being finalized during install - that the /dev/sdc1 /boot partition was somehow given priority to the /dev/md0 /boot "array" - and, therefore, added to fstab (and assigned some grub) by the installer while /dev/md0 was not?

3. Might it just be a "simple" matter of making certain that grub is properly installed or configured on the /dev/md0 array?

4. How can I tell whether things are (already) set up properly - grub-wise?

5. Might it just be a "simple" matter of adding the /dev/md0 array to fstab?

6. Any thoughts as to why /dev/md0 would not have been added to fstab during install?

7. Can multiple /boot partitions share a single fstab file?

Thanks for any insights....

April 27th, 2009, 04:50 PM
Following-up on my original post (and with reference to this configuration (http://ubuntuforums.org/showpost.php?p=7134682&postcount=4)):

8. According to blkid -L, the bootable md0 array (consisting of bootable partitions sda1 and sdb1) is not mounted. Could this be a reason that (hd0,0) and (hd1,0) don't show up when I run ">grub find /grub/stage1"?

9. How can I find out whether grub is properly installed on the unmounted md0 array?

9.a. Could I temporarily mount (and then umount) the md0 raid array into a random "/findtest" directory for the purposes of having ">grub find" take a look to see if the grub files are present within the array?

10. Might a simple commenting out or replacement of sdc1 in fstab with /dev/md0 be the solution to getting the system to boot from md0?

10.a. I would like to use a uuid for /dev/md0 in fstab - would the uuid I enter for "/dev/md0" be that of "md0"? Or would the uuid of "/dev/md0" be that of "sda1" - which is the "primary" bootable partition of the md0 array? Should I not use a uuid for /dev/md0 in fstab?

11. Does "dev/sdc1" need to be removed or commented out of fstab - or can it be re-assigned to another mount point - rendering it accessible (at boot) - if need be (see 12. and 13.)?

NOTE: Before I revise fstab and reboot:

12. I'd like to set up a fallback (http://www.gnu.org/software/grub/manual/grub.html#Booting-fallback-systems) situation - where if the md0 array won't boot (as I now try to configure it properly - or sometime in the future) the system could be directed to boot from sdc1 - which I know works. The issue is how do I make sdc1 "bootable" without adding it to /boot in fstab? Would grub be able to boot from sdc1 if sdc1 (or it's uuid) were present in menu.lst, but not in fstab?

13. Can I just set up a situation where the grub menu (at boot via ESC) gives me the option to boot from either the raid array (md0) or the vanilla partition (sdc1)?

Thanks for any guidance!

April 28th, 2009, 07:14 PM
...with the aid of large swaths of google, I feel I might finally be approaching a practical resolution to this grub issue.

Here's a preliminary framework:

h. Create a grub-bootable "rescue" cd-rom (stage2_eltorito) (http://www.gnu.org/software/grub/manual/html_node/Making-a-GRUB-bootable-CD-ROM.html)

i. Test the rescue cd-rom to see whether it works as I think it should - i.e. boots into my system exactly the way it would if I were booting from my hard drive....

j. Reboot the system without the rescue cd-rom

k. Add the active/bootable /dev/md0 (sda1 and sdb1) array to fstab at the mount point /boot

l. Keep the active/bootable /dev/sdc1 parition in fstab at the mount point /boot

m. Modify menu.lst to set /dev/md0 as the default boot entry.

n. Modify menu.lst to set /dev/sdc1 as the fallback boot entry.

o. Reboot and be done (with this task)....


14. Given that the active partitions /dev/md0 and /dev/sdc1 are ("legally") on separate drives, why then was /dev/md0 NOT automatically added to fstab during install? Can two arrays or partitions (even though on separate disks) not share the same mount point "title" (e.g. /boot)?

15. Restated: Is it possible for /dev/md0 and /dev/sdc1 to share the same mount point in fstab?

16. Will I need to "update-grub" menu.lst, somehow, in order for my manually-entered menu.lst changes to take effect? Or, should this "update-grub" happen, automatically, at reboot?

17. Is there anything I am missing?

Thanks for any knowledge....

May 1st, 2009, 10:31 PM
Any comments?

May 3rd, 2009, 01:58 PM
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