I have two RPi3 OMV3 installations which each have an SSD for booting and OMV, then a data disk HDD. When I use root=/dev/sda2 in /boot/cmdline.txt OMV tries to use the data disk HDD as the root device, rather than the SSD when the HDD is connected, but works fine when it is not. I have tried put the UUID in /etc/fstab and tried using root=UUID=ae708a4d-982a-4a20-965c-01ec7e1f32b3 in cmdline.txt, but the boot just hangs. This happens even if I disconnect the HDD before powering up.
It looks like OMV does not like UUID for booting, or this is not supported but it is very hard to figure out which it is. Is there a simple reliable way of making sure the right partition is used as root when booting? I suppose I could try pointing to /dev/sdb2 and see if that works, but I would rather have a foolproof setup if possible.
ARMBIAN 5.42 experimental Debian GNU/Linux 8 (jessie) 4.14.30-v7+