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195 points tosh | 2 comments | | HN request time: 0.425s | source
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shivak ◴[] No.42208324[source]
> > The power shelf distributes DC power up and down the rack via a bus bar. This eliminates the 70 total AC power supplies found in an equivalent legacy server rack within 32 servers, two top-of-rack switches, and one out-of-band switch, each with two AC power supplies

This creates a single point of failure, trading robustness for efficiency. There's nothing wrong with that, but software/ops might have to accommodate by making the opposite tradeoff. In general, the cost savings advertised by cloud infrastructure should be more holistic.

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dralley ◴[] No.42208722[source]
>This creates a single point of failure, trading robustness for efficiency. There's nothing wrong with that, but software/ops might have to accommodate by making the opposite tradeoff.

I'll happily take a single high qualify power supply (which may have internal redundancy FWIW) over 70 much more cheaply made power supplies that stress other parts of my datacenter via sheer inefficiency, and also costs more in aggregate. Nobody drives down the highway with 10 spare tires for their SUV.

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shivak ◴[] No.42209079[source]
A DC busbar can propagate a short circuit across the rack, and DC circuit protection is harder than AC. So of course each server now needs its own current limiter, or a cheap fuse.

But I’m not debating the merits of this engineering tradeoff - which seems fine, and pretty widely adopted - just its advertisement. The healthcare industry understands the importance of assessing clinical endpoints (like mortality) rather than surrogate measures (like lab results). Whenever we replace “legacy” with “cloud”, it’d be nice to estimate the change in TCO.

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malfist ◴[] No.42209567[source]
DC circuit protection is absolutely not harder than AC. DC has the advantage in current flowing in only one direction, not two
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1. paddy_m ◴[] No.42209948[source]
Which makes it much harder to break the circuit vs AC
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2. wbl ◴[] No.42210571[source]
At 48 volts arcing shorts aren't the concern.