Comments on: Fixing a degraded Linux software RAID-1 mirror

By: Preston

Preston — Sun, 29 Mar 2009 06:17:25 +0000

Great article!

I wanted to upgrade my boot RAID on my home server from 160GB drives to 1TB drives, but kept on coming unstuck at boot after replacing the first disk. Turned out I needed to copy the MBR as per the start of your instructions – I’d (maybe crazily?) assumed that doing a grub install would do that.

You saved me a lot of hassle, thanks.

By: reader

reader — Fri, 06 Mar 2009 16:41:04 +0000

great article. worked like a charm for me. THANKS !

By: Dennis Krul

Dennis Krul — Sat, 09 Jun 2007 12:30:50 +0000

I think that only works if your first drive is completely removed from the system, so the second drive becomes (hd0). If you don’t remove the disk GRUB will search for the stagefiles and the menu.lst on the first disk, which is faulty, and thus you can’t boot.
You could however do something like this (in grub’s menu.lst):
# Default boot title Linux (hd0,0) kernel (hd0,0)/bzImage root=/dev/md1

# Fallback if (hd0,0)/bzImage is unreadable
title Linux (hd1,0)
kernel (hd1,0)/bzImage root=/dev/md1
With Lilo you don’t have to specifically point to a physical device. You can just point to the MD device, which is (in my opinion) a cleaner solution.

Maybe I should have explained that in more detail in my post Thanks for the suggestion though.

By: ruben

ruben — Fri, 08 Jun 2007 19:12:55 +0000

What went wrong with Grub? You copied the MBR from sda to sdb, so grub should work, or am I missing something?

Grub>device (hd0) /dev/sdb
Grub>root (hd0,0)
Grub>setup (hd0)

should do the trick as well.