Can't boot after converting lvm2 root to lvm2 raid1

Question

I have Ubuntu 12.10 (no updates, kernel 3.5.0-17-generic) on first HDD (sda), which uses MBR and was partitioned as "Use whole disk for ubuntu" with LVM2 enabled. Root filesystem is on LVM2 (VG:ubuntu). Today I added second HDD (sdb) with same size, partitioned it like first hdd, created lvm2 PV and converted root LV to raid1:

pvcreate /dev/sdb5
vgextend ubuntu /dev/sdb5
lvconvert --type raid1 -m1 /dev/ubuntu/root /dev/sdb5

After 100% resync I rebooted and initramfs was unable to find root fs:

Begin: Running /scripts/init-premount ... done.
Begin: Mounting root file system ... Begin: Running /scripts/local-top ... done.
... (kernel messages)
Gave up waiting for root device. Common problems:
 - Boot args (cat /proc/cmdline)
   - Check rootdelay= (did the system wait long enough?)
   - Check root= (did the system wait for the right device?)
 - Missing modules (cat /proc/modules; ls /dev)
ALERT!  /dev/mapper/ubuntu-root does not exist.  
Dropping to a shell!

There is list of modules:

(initramfs) cat /proc/modules
hid_generic
usbhid
hid
e1000
raid10
raid456
async_pq
async_xor
xor
async_memcpy
async_raid6_recov
raid6_pq
async_tx
raid1
raid0
multipath
linear
(initramfs) cat /proc/cmdline
BOOT_IMAGE=/vmlinux-3.5.0-17-generic root=/dev/mapper/ubuntu-root ro
(initramfs) ls /dev/mapper
control     ubuntu-swap_1

There is output from lvm utility:

lvm> pvscan
  PV /dev/sda5    VG ubuntu   lvm2 [ 13.76 GiB / 408.00 MiB free]
  PV /dev/sdb5    VG ubuntu   lvm2 [ 13.76 GiB / 508.00 MiB free]
lvm> vgscan
  Reading all physical volumes. This may take a while...
  Found volume group "ubuntu" using metadata type lvm2
lvm> lvscan
  inactive        '/dev/ubuntu/root' [13.26 GiB] inherit
  ACTIVE          '/dev/ubuntu/swap_1' [100.00 MiB] inherit

lvm> lvdisplay ubuntu
  --- Logical volume ---
  LV Path                /dev/ubuntu/root
  LV Name                root
  VG Name                ubuntu
  LV UUID                xxxxxxxxxxxxxxx
  LV Write Access        read/write
  LV Creation host, time ubuntu, 2013-05-07
  LV Status              NOT available          <<<<< !!!!
  LV Size                13.26 GB
  Current LE             3394
  Mirrored volumes       2
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto

And lvchange -ay ubuntu fails:

lvm>  lvchange -ay ubuntu
  /sbin/modprobe failed: 1
  Can't process LV root: raid1 target support missing from kernel?

What is missing from initrd?

Answer 1

I hit this same problem on my Debian system; it turned to be caused by some necessary modules not getting installed in the initramfs.

Specifically, after adding these lines to /etc/initramfs-tools/modules:

dm_mirror
dm_raid
dm_region_hash

and running

update-initramfs -u -k all

my system boots correctly.

Note that I have not checked that all of these lines are actually necessary. I think the dm_raid module is missing by default at least.

After further searching, there is a Debian bug open against initramfs-tools over this issue: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=699804

Answer 2

Another option is to use the mirror type instead of the raid1. That should work by default, even grub2 supports it. So instead of

lvconvert --type raid1 -m1 /dev/ubuntu/root /dev/sdb5

do this:

lvconvert --type mirror -m1 /dev/ubuntu/root /dev/sdb5

(You don't need to specify sdb5 at the end, LVM will choose a suitable PV to put the mirror on.)

The mirror type has a big drawback though, it only reads from the first device, so you won't get the read performance speedup expected from RAID1.