Comment Coherence (Score 3, Insightful) 23
When I was working for a startup in the early 2000s, we had our own servers. We were growing, so were adding servers at a pretty good clip. After one particular expansion, all of a sudden, Saturday night at 3 am, we blew breaker. No one had a good explanation, but the sysadmins were not happy about needing to go to the office in the middle of the night to fix things up.
A week later, the same thing happened. I suggested that it was the RAID check kickoff that might be doing it. And, indeed, it was. A couple of dozen servers all seeking their drives at once was too much for the circuits they were on. Staggering the startup time fixed it.
Coherence can be good, like when you're rowing crew, or bad, like when you have dozens of drives all drawing max power. Or, from the summary, gazoober UPS systems doing a battery check.