ZFS based root volume (zroot)
Bhyve based instance
By default, /data/ is mounted with the extra disk. If you would like to add this to you zfs zroot pool you will need to make a few changes.
vi /etc/fstab . (and remove the /data/ mount point)
Destry the gpt partitioning on /dev/vtbd1 by running: # gpart destroy -F /dev/vtbd1
Extend the zpool by running: # zpool add zroot vtbd1