VAXen - it was easy then too
I watched a guy who had just come back from a VAX/VMS system admin course trying to set up mirrored disk - what DEC called RAID-1.
Before I could stop him, he had mirrored the system disk with a blank disk, but had the blank disk as the master. We watched as the system slowly evaporated and crashed.
Ahh an evening with TU45's loading VMS again.