Grub2: Disk not found trying to boot LVM partition on raid1 set

Question

I'm having difficulty booting from an LVM logical volume which is stored on a raid-1 physical volume. Using Ubuntu 13.10 and Grub2 2.00.

The setup is that /boot/grub is on a physical raid-1 set. This all works fine to boot linux from another physical raid-1 disk. I've added another ubuntu installation (14.04) on an lvm volume (also on a raid-1 physical volume), intending to extend the volume if I run out of space on the root partition. This new ubuntu partition boots fine under kvm, and was recognised by update-grub and added to the grub menu

When I try and boot the new partition on my physical PC, I see the grub menu, select the new partition and try to boot, which results in the following errors:

error: no such device: <uuid> 
error: disk lvm/vg-lvname not found
error: you need to load the kernel first

I see that

root=lvm/vg-lvname

(with the names of my vg and lv), and

prefix=(dm2,0)/boot/grub

Note that the quotes above are included in the response to the set command. If I do ls, I can see all my dm0 etc and physical disks, but no lvm disks show up

ls lvm[tab] 

doesn't find anything.

lsmod 

shows that all the modules I think are needed (lvm, dmraid, mspart09) are loaded

The menu entry in grub.cfg is:

menuentry 'Ubuntu 14.04 LTS (14.04)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-simple-b38e71af-fffb-4525-ba66-be153a34dc17' {
    insmod part_msdos
    insmod part_msdos
    insmod part_msdos
    insmod part_msdos
    insmod part_msdos
    insmod part_msdos
    insmod diskfilter
    insmod mdraid09
    insmod diskfilter
    insmod mdraid09
    insmod diskfilter
    insmod mdraid09
    insmod lvm
    insmod ext2
    set root='lvm/vg1-rootfs2'
    if [ x$feature_platform_search_hint = xy ]; then
      search --no-floppy --fs-uuid --set=root --hint='lvm/vg1-rootfs2'  b38e71af-fffb-4525-ba66-be153a34dc17
    else
      search --no-floppy --fs-uuid --set=root b38e71af-fffb-4525-ba66-be153a34dc17
    fi
    linux /boot/vmlinuz-3.13.0-24-generic root=UUID=b38e71af-fffb-4525-ba66-be153a34dc17 ro nosplash
    initrd /boot/initrd.img-3.13.0-24-generic
}

so it seems to be failing on the search command; not finding the uuid, then on the linux command, not finding the volume in the root command, then on the initrd command because it failed to load a linux module

I'd appreciate any advice please.

Answer 1

Solution found: I discovered that I needed to re-install grub to the boot drive (sudo grub-install --modules='lvm mdraid09' /dev/sda and ditto for /dev/sdb as they are mirrored), after which it found my lvm device and loaded the kernel & initramfs.

Now the next step is to get the raid arrays to start so it can find the root volume - by installing mdadm I think but think I'm ok on this & will ask if I need help