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Comment by growse | Hacker News Reader

> 1. Dual power in each server/device - One PSU was powered by one outlet, the other PSU by a different one with a different source meaning that we can lose a single power supply/circuit and nothing happens

Nothing happens if you remember that your new capacity limit per DC supply is 50% of the actual limit, and you're 100% confident that either of your supplies can seamlessly handle their load suddenly increasing by 100%.

I've seen more than one failure in a DC where they wired it up as you described, had a whole power side fail, followed by the other side promptly also failing because it couldn't handle the sudden new load placed on it.

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EDIT: I misunderstood you were talking about power feeds, the normal case is the run "48% as if it's 100%" (because of power spikes, but also most types of transformers run more efficiently under specific levels of load (40-60).

Normally this is factored into the Rack you buy from a hardware provider, they will tell you that you have 10A or 16A on each feed, if you exceed that: it will work, but you are overloading their feed and they might complain about it.

OP is talking about the DC power feed, not a single server PSU.

You don't get fed DC power, you get fed AC power.

But, point taken: yes your power feed should be running at <50%. But that just means you treat 50% as 100% just like any resource.

Mostly this is outsourced to the datacenter provider; they'll give you a per side rating. (usually 10A or 16A) which also matches the cooling profile of the cabinet.

I mean, in some datacenters they run DC power to each rack. Its definitely more esoteric than having each device run AC but some people do it.

However, with their comment DC == Data Center, not Direct Current.

Yeah, I got thrown off by the "per DC supply is 50% of the actual limit"

DC = Datacenter? makes no sense, so my head replaced it with "Power Supply" instead of "DC Supply", second sentence does make sense as being datacenter though.

The poster was speaking more of the power delivery going to the power supplies, not the server's power supplies themselves. So say each PSU 1 is wired to circuit A, each PSU 2 is wired to circuit B. Circuit A experiences a failure. All servers instantly switch over all their load to their PSU 2's on circuit B. Suddenly circuit B's load is roughly double what it was just moments ago. If proper planning wasn't created or followed, this might overload circuit B, meaning all PSU 2's go dark regardless of the server being able to do the change over or not.

Yeah I understand on re-reading: but that's also not how people run datacenters.

Obviously people can operate things however they want, but you wont get a tier 3 classification with that setup.

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