The reason: Grub code was written to the Master Boot Record (MBR) of the first drive. That code points to the grub menu in the second drive. But if it’s not connected it goes nowhere and you get an error of course.
Here are three options:
- Put a tiny boot partition on drive 1 and transfer the contents of the Linux directory /boot to that partition. The grub menu is in the /boot directory so it will always be available, despite whether drive 2 is connected or not
- Switch back to booting by using windows bootloader. Put windows code back in the MBR of drive 1. Add the instruction to boot Suse ias an option in the windows bootloader. The windows bootloader resides on drive 1.
- Use the menu from the bios to choose whether to boot from drive 1 or drive 2 — on my computer it’s the F11 key that makes the menu pop up. Put the Suse bootloader into the MBR of drive 2. Put the windows bootloader into the MBR of drive 1. Select which to boot essentially from thr F11 key (or whatever key it is for you).