[gerdesj]

"Sounds like a plane taking off."

Helicopter. I live in Yeovil, Somerset, UK - there's a helicopter factory just down the road. I had a IBM "AS/400" or whatever they are called now in our computer room rack for a customer and it made nearly as much noise as everything else put together. It was clearly tuned for start up noise to impress because they would fire up in sequence, rise to a crescendo and then slow down in sequence to just a din instead of painfully loud.

A switch or PC server on boot will normally run up cooling fans instantly to max as a default protection mechanism until the "OS" has started and sensors read and then the fans will slow down to deal with the actual thermal load.

If you switch off your air conn, it gets noisy, quickly. Recently in the UK we are seeing routine temperatures around 30C and we broke 200 odd year records for temperatures a few weeks back. I know its even worse elsewhere but our infrastructure is not designed for this. Here we are at the same latitude as Calgary AB!

[LargoLasskhyfv]

That's called staggered spin-up. One does that for sets of HDDs, too.

Anyway, what is it good for? To not overload the PSU for one, because spin-up needs more energy, until it has reached it's intended range of RPM. (for fans & HDDs)

Another reason to spin-up high initially, to fall down to slower when up, is to overcome friction in the bearings, to get stuck things unstuck, and shake dust off. (for fans)

[gerdesj]

Tell that to my switches and PC servers. They all spin up their fans in one go as soon as power good is received and the initial BIOS thingie has stubbed out its fag on the floor.

The PSUs are painting their nails when the fans go off initially. The GPUs, RAID controllers and co are still waking up.

A further counter example is an Equallogic PS6500. That has 48 3.5" spindles in it and three PSUs plus a few fans and two controllers. The whole thing boots in a couple of minutes.