[CentOS] Software RAID + LVM + Grub

Matthew Topper topperm9 at gmail.com
Sat Sep 18 14:41:47 EDT 2010


Entering those commands exactly worked, but I'm not sure why it
worked.  So, it's progress.

I need to find some good reference on GRUB, which seems difficult
because most things I can find are about GRUB2, and CentOS has 0.97

On Sat, 18 Sep 2010 17:42:59 +0200
Timo Schoeler <timo.schoeler at riscworks.net> wrote:

> 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.
> 
> http://wiki.centos.org/HowTos/CentOS5ConvertToRAID#head-fa2b73a28acdf965daa1e018962eaa8cbd94110c
> 
> HTH,
> 
> Timo :)
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