Thank you for the help --bgeddy (as always) and guanx -- in a previous thread I asked for help, concerning this topic, however, I feel that I've changed my approach enough to warrant a new thread.
Hi, empcrono - and thanks for the nice words.
I originally replied to your thread as I spent some time trying to get Slackware to boot from an external USB hard disk - the process taught me a lot but was frustrating!
If your PC is capable of booting from a USB device then all you should need is lilo/grub as the bootloader to boot any Linux versions - with the prior mentioned provisos.
The main things I have found to make a USB attached device boot up are:
1) Set the BIOS/boot selection to boot from an external USB device.
2) Add the "rootdelay=" to lilo.conf to allow the boot to wait for the drive to come up.
3) Add the USB modules to any initial ram disk that you may be booting with.
4) guanx made a valid point in your original thread
that I overlooked as my external USB drive always gets assigned that same drive name - I don't have many USB devices that I mess with. However when I have played with plugging other devices this change of assignment has caught me out - the UUID was the solution I used. In other word your external USN drive may not always appear as /dev/sdd - depending on what is attached.
Unfortunately, as is so often the case with IT setups, this depiction may not fit your case. The main thing to check is, again, whether your machine can boot from a USB device, If so then the rest should just be a process off elimination.
If it's any consolation - I bought a new 1TB external USB disk a little while ago and came to the conclusion that I could not boot from it. I had tried installations which where successful but I just could not boot - until I figured out the rootdelay and Bios boot device selection options. This is the system I now use daily. It's always easy when you know how
I hope your situation is similar.