Booting from USB on RPI3

[Jonathan Chen]

On Fri, 24 Apr 2020 at 08:22, Mark Millard <marklmi at yahoo.com> wrote:
[...]
> The RPi3 will not start to boot from a gpt partitioned
> media. So picking gpt labeling as the example is somewhat
> misleading for single-media booting. glabel based
> labeling would be more realistic for the context.

The OP is attempting to boot off an external USB drive via loader.env.
So it's the external drive's partitioning system that is of interest.
FYI, my RPI3 boots off a GPT partition fine:

1.topaz:~,8:30am# uname -a
FreeBSD topaz.inside.chen.org.nz 12.1-STABLE FreeBSD 12.1-STABLE #0
r358927: Sun Mar 15 22:24:30 NZDT 2020
jonc at onyx.inside.chen.org.nz:/xbuilds/rpi3/obj/usr/src/arm64.aarch64/sys/GENERIC
 arm64
1.topaz:~,8:30am# gpart show -l da0
=>       40  976773088  da0  GPT  (466G)
         40       8152       - free -  (4.0M)
       8192  964689920    1  topaz-root  (460G)
  964698112   12075016    2  topaz-swap  (5.8G)

1.topaz:~,8:30am# cat /etc/fstab
# Device                Mountpoint      FStype  Options         Dump    Pass#
/dev/gpt/topaz-root     /               ufs     rw              1       1
/dev/gpt/topaz-swap     none            swap    sw              0       0

Cheers.
-- 
Jonathan Chen <jonc at chen.org.nz>