Debian: How to boot from btrfs root on LVM on USB?

Question

Using debootstrap I have installed a Debian wheezy system on an external USB drive with the following partitioning layout:

/dev/sda: GRUB in MBR
  L sda1: ext2, /boot
  L sda2: LVM PV
      L VolGroup vg0
          L lv0: btrfs, /
          L lv1: ext4, /tmp
          L lv2: swap

When I try to boot this setup, I get dumped in the initramfs-Shell saying that the root fs could not be found. A simple vgchange -ay; exit brings the system up fine, but obviously I do not want to do this every time I boot.

Looking at the initramfs output I see that the LVM hook does not find the 'vg0' VolGroup. After this message I see the kernel messages for the recognition of my external drive.
So I suspect that the problem is the USB drive getting recognized too late for the LVM stuff to detect and activate the VolGroup.

How do I make the LVM hook wait for my USB drive to get recognized?

Thanks in advance!

Answer 1

Mea culpa, found the trivial solution: rootdelay=5 in kernel cmdline fixed it.