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.