Created attachment 169014 [details]
On the machine described by the attached dmesg, installing 10.3 RELEASE (in Bugzilla, despite the fact that 10.3 has been released, I can only choose 10.3-BETA2; this is not good) using ZFS root and GPT without UEFI results in a non-bootable system. Doing the same install with an MSDOS partition table does boot.
Try choosing the partitioning option 'GPT + Active' and see if that satisfies your hardware. Likely an odd BIOS implementation.
(In reply to Allan Jude from comment #1)
As I said in my original post, I did get the system to boot by using an MSDOS parition table. But other issues with FreeBSD on this machine (X won't come up with the ATI driver; have to use VESA) led me to install DragonFly, which is working well. I'm not going to blow away that install to test your hypothesis. The machine has an Asus motherboard, so it's mainstream stuff (which doesn't prove the BIOS is bug-free, but it's not from some fringe m-board maker) and I've run Arch Linux on this machine with a GPT partition table with no trouble.
What I will do to try to help debug this is, when I have time, I will repeat the install that wouldn't boot on a spare USB drive. If I can reproduce the problem, then I will re-install using your suggestion and report what happens.
I note, by the way, that GPT without UEFI is the installer's default when you choose ZFS root.
(In reply to donaldcallen from comment #2)
Yes, GPT without UEFI was the default. The default is now GPT with UEFI if you booted the installer UEFI, and GPT without (CSM/BIOS), if you booted BIOS.
The only machines I've seen have trouble with GPT + BIOS are are specific series of Lenovo notebooks (T420, T520, etc)
I know a few HP and Dell machines require the 'active' setting.
I am not aware of any Asus boards not working as expected.