I installed NetBSD on the entire second disk which happens to be a small solid state drive (intended for windows and making it faster). Simple searching turned up nothing about how to get this to work with grub2 (some things refer to grub1 and others refer to netbsd sharing the first disk). For reference here's the answer:
[...]# cat /etc/grub.d/42_custom #!/bin/sh exec tail -n +3 $0 # This file provides an easy way to add custom menu entries. Simply type the # menu entries you want to add after this comment. Be careful not to change # the 'exec tail' line above. menuentry "NetBSD on sda1" { set root=(hd1,1) chainloader +1 } [...]# grub2-mkconfig -o /boot/grub2/grub.cfg Andrew