Problem with installing LL-only (single boot) to Samsung 850 EVO SSD

[m654321]

Don't use a separate boot partition. Grub should be at the beginning of the first partition on the disk. The message is just a prompt for windows rescue media because your computer can't find the disk. It's been my experience that if you try to use a separate boot partition on some computers, even with legacy mode enabled, the BIOS will not find the disk. This is because the UEFI loader is still the default whether or not you enable legacy mode; legacy is just an added feature; thus the system looks for Windows disks first; thus the prompt, because Windows defaults to the media channel when disks are unavailable. There are tricks to get around this, not too difficult, but since you have already succeeded I won't go through them.
TC 

Thanks Trinidad - I've never used a separate /boot partition - was just querying it, though had half-assumed it wasn't necessary.  Many thanks too for your explanation as to why my UEFI laptop doesn't recognise a GPT formatted SSD that has only LL installed on it, i.e. without a Windows OS installed alongside it.  This makes perfect sense.

Cheers
Mike