Other Where am I booting from?

[balanga]

(Note to self...) I guess if change BIOS to legacy only, the disk won't boot... I'll see in a moment....

And it didn't so mystery solved...

 

[balanga]

This is just a GPT "protective MBR" without any boot code. For UEFI-only booting, this is correct.

So, how does the system know where to look for any boot code?

 

[zirias@]

So, how does the system know where to look for any boot code?

"Legacy" boot just loads the MBR and executes the code from there. It won't work on this disk as your MBR doesn't contain any code (all zeroes). This code can't be any larger than 446 bytes, so it can do almost nothing and typically needs another more capable bootloader to chainload from somwhere. With FreeBSD's MBR bootcode for booting from GPT (/boot/pmbr), this would be the first partition of type freebsd-boot.

UEFI boot looks for a partition of type efi with a FAT filesystem and loads and executes a file from there. If not configured otherwise, this is e.g. efi/boot/bootx64.efi on amd64.

You can support both methods at the same time.