Booting from alternate hard drive

[Chris Jones]

I have a laptop with two hard drives and with debian/stable as the main
OS - that's where I keep my grub environment. 

This main debian/stable OS resides on disk SDA together with the other
linux installs I occasionally boot into.

Having run out of space on SDA I installed another flavor of linux
(Deepin) on the laptop's second drive (SDB)

As per "fdisk -l" identifies it as /dev/sdb10. 

I was able to mount this partition from the debian/stable system and the
contents are indeed as intended.

In order to boot this new system I proceeded to add the following to my
/etc/grub.d/40_custom config file:

menuentry " Deepin 15.5 - 64bit, with Linux 4.9.0-deepin13-amd64 (on 
/dev/sdb10)" {
  insmod gzio
  insmod part_msdos
  insmod ext2
  set root='(hd1,msdos10)'
  search --no-floppy --fs-uuid --set=root 60e5f04d-419c-4ceb-a0d2-09fcf36e30c3
  linux /boot/vmlinuz-4.9.0-deepin13-amd64 
root=UUID=60e5f04d-419c-4ceb-a0d2-09fcf36e30c3 ro reboot=pci
}

I ran update-grub and restarted the box and the new entry was indeed
visible in grub's chooser/menu.

Unfortunately, when I select the Deepin entry I end up with some kind of
kernel panic.

As far as I understand it... grub is installed in the MBR of the two
drives (I ran dpkg-reconfigure grub on this debian sysstem and both
devices were listed).

Any suggestions as to what I should check (and how) and what I might try
to narrow down the issue...?

Thanks,

CJ