What partition should grub be installed on?

Question

Debian

Hetzner's server with debian
Once again did the usual apt-get upgrade. It
gave out such nonsense:

What to do, which partition to choose so that the server does not die?

Answer 1

GRUB (1st stage) is placed not in the partition, but on the boot disk in the gap between the MBR and the beginning of the first partition. So most likely /dev/sda.

Answer 2

with a space, check /dev/sda and /dev/sdb