How to boot from a lvm root disk:
set timeout=2 set root=(VGSys00-LVRoot00) insmod linux menuentry "Linux" { linux /boot/vmlinuz root=/dev/ram0 lvmroot=/dev/VGSys00/LVRoot01 initrd /boot/finitrd }
If any physical volumes of your logical root volume are missing, then you have to call lvm commands with the -P or --partial flag. All logical volumes on errorneous volume groups are in ready-only state, even if you have setup a mirrored logical volume (aka soft RAID-1). Calling blockdev --setrw /dev/VGSys00/LVRoot01 may help in such a situation.