[CentOS] Software RAID + LVM + Grub

Timo Schoeler timo.schoeler at riscworks.net
Sat Sep 18 11:42:59 EDT 2010

On 09/18/2010 05:13 PM, Matthew Topper wrote:
> I'm playing with software RAID and LVM in some virtual machines and
> I've run into an issue that I can't find a good answer to in the docs.
> I have the following RAID setup:
> md0: sda1 and sdb1, RAID 1.  This is /boot
> md1: sda2 and sdb2, RAID 1.  This is a PV for LVM.
> VolGroup00, this is the volume group and md1 is the only PV in it.
> LogVol00 is swap
> LogVol01 is /
> LogVol02 is /home
> So, I tested to see what happens if I disable sdb in virtualbox.
> Machine booted find and I was able to see that part of the raid array
> was gone.
> I reattached the disk and rebuilt the array
> mdam --add /dev/md0 /dev/sdb1
> mdam --add /dev/md1 /dev/sdb2
> The array rebuilt without issue.  But now, if I remove sda, the machine
> doesn't boot and grub complains.  The question I have is how does one
> reinstall the boot sector at this point?  I'm a little confused as far
> as to what device to install it on and what to specify as the root.
> This is grub.conf if it helps:
> default=0
> timeout=5
> splashimage=(hd0,0)/grub/splash.xpm.gz
> title CentOS (2.6.18-194.e15)
> 	root (hd0,0)
> 	kernel /vmlinuz-2.6.18-194.e15 ro root=/dev/VolGroup00/LogVol01
> 	initrd /initrd-2.6.18-194.e15.img
> Grub has always been a little confusing for me, so I guess I don't
> understand.  What do the two root entries specify?  And again, my main
> question is how do I reinstall grub to the repaired disk?  Sorry for
> the lengthy post, I'm trying to provide as much information as possible.



Timo :)

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