The Nimble V5 doesn't seem to properly boot FreeBSD when it lies on a partition larger than roughly 200GB. The error manifests as either a 'Cannot find /boot/loader' or a forever-spinning pinwheel when it tries actually booting the kernel.
To get around this when you want a single large partition, place /boot on a separate partition! This requires some dinking around, because the kernel assumes that the partition it's loaded from is the root partition.
Sysinstall cannot properly create this, as it assumes root is always the 'a' partition. Unfortunately, the boot stuff assumes /boot will be on the 'a' partition, and that's much more difficult to change. So, after installation, switch the partition names:
a: 1048576 16 4.2BSD b: 4194304 1048592 swap c: 976562500 0 unused d: 971319604 5242896 4.2BSD
In /boot, move boot out of the way, and replace with a symlink to ., so that the loader can find everything automatically when it looks in /boot.
# cd /boot # mv boot boot.block # ln -svf . boot
Tell the first boot stage where the stage 3 loader can be found, as it can't understand symlinks:
# echo "0:ad(0,a)/loader" > /boot/boot.config
Tell the kernel where to find the proper root device, via a dummy fstab:
# mkdir -p /boot/etc # echo "/dev/ad0d / ufs rw 1 1" > /boot/etc/fstab
Handle any unexpected problems. >.^<