Think about this: You are in the hospital and you are allergic to at least three meds and, because now they just put a sticker on your id bracelet that you are “allergic to something”, the hospital has SERVER PROBLEMS and they can’t access anyone’s medical records. HOW ARE THEY GOING TO FIND OUT WHAT YOU ARE ALLERGIC TO?
It’s called HA - High Availability. Replicated servers in case on goes down.