The big companies have millions of servers. At that scale, they have software teams monitoring every part of the datacenter from temperatures on each server/ra

The big companies have millions of servers. At that scale, they have software teams monitoring every part of the datacenter from temperatures on each server/rack down to where every drive is at and their health. It is also highly automated with systems to direct technicians on what/where/how to repair broken parts and thus they don't have people just patrolling racks looking for problems. They also have special badges to access the data centers so people generally cannot just visit datacenters as only a select few people with business justification can visit them.