# fetch https://opnsense-mirror.hiho.ch/releases/mirror/OPNsense-20.1-OpenSSL-nano-amd64.img.bz2 -v -o - | bunzip2 | dd bs=1M of=/dev/ada0
[...]
# fsck /dev/ada0a
** /dev/ada0a
** Last Mounted on
** Phase 1 - Check Blocks and Sizes
CYLINDER GROUP 0: BAD MAGIC NUMBER
REBUILD CYLINDER GROUP? [yn] ^C