Long story short: I've got an old zx6000, running RHEL/CentOS (cannot recall which one) IA64 v4.x and moved its two-drive mirror set to another matching unit - but I cannot find any EFI shell ...
I'm running a Supermicro C7Z170M. Generally works OK, except when there's any significant Windows update. if there is, then 10 times out of 10, when Windows 10 reboots I'll get dumped to an EFI shell.