Identical device not big enough for mirrored boot?

[kdragon75]

Booting from USB will eat your zpool and kill your first bourn. Also boot from USB is perfectly reliable and works fine.

Edit: just like ECC memory

 

[28061]

What board do you have?

Supermicro X10SL7-F

All of the USB ports used are the hardwired ports fixed on the motherboard. No extensions, case slots or card reader devices used.