pfSense

That's an issue with Xen changing your devices without telling you, and coupled with FreeBSD's Xen disk driver not also offering a symlink to the legacy device name. Nothing we can automatically do to detect/handle that.

You can, pre-upgrade, run /usr/local/sbin/ufslabels.sh and have it adjust the fstab file to use UFS labels rather than device names and the upgrade will succeed as far as the disk is concerned. But it may also change your NIC types on you, which we also can't account for, so you'd have to reassign the NICs, too.

With Xen you're better off making a new VM and installing 2.2 fresh.