The firmware included with the Raspberry Pi 2 Model B version 1.2 introduced the possibility of booting from a USB device: before that, it was only possible to boot from an SD or microSD card. But ...
Your PC might mistakenly detect external drives, removable media (USB devices or non-bootable discs), etc., as bootable devices and attempt to boot from them. In this case, remove or disconnect ...
I have a Supermicro X11SCL-IF, which has run TrueNAS for several years, UEFI booting off a pair of small SSDs. All the drives for the TrueNAS install are connected to the usual suspect, an LSI HBA in ...