This past Saturday (yesterday as I write this), a university machine room had an AC failure of some kind :

It's always fun times to see a machine room temperature of 54C and slowly climbing. It's not our machine room but we have switches there, and I have a suspicion that some of them will be ex-switches by the time this is over.

This machine room and its AC has what you could call a history; in 2011 it flooded partly due to an AC failure , then in 2016 it had another AC issue , and another in 2024 (and those are just the ones I remember and can find entries for).

Most of this machine room is a bunch of servers from another department, and my assumption is that they are what created all of the heat when the AC failed. Both we and the other department have switches in the room, but networking equipment is usually relatively low-heat compared to active servers. So I found it interesting that the temperature graph rises in a smooth arc to its maximum temperature (and then drops abruptly, presumably as the AC starts to get fixed). To me this suggests that many of the servers in the room kept running, despite the ambient temperature hitting 54C (and their internal temperatures undoubtedly being much higher). If some servers powered off from the heat, it wasn't enough to stabilized the heat level of the room; it was still increasing right up to when it started dropping rapidly.

(Servers may well have started thermally throttling various things, and it's possible that some of them crashed without powering off and thus potentially without reducing the heat load. I have second hand information that some UPS units reported battery overheating.)

It's one thing to be fairly confident that server thermal limits are set unrealistically high . It's another thing to see servers (probably) keep operating at 54C, rather than fall over with various sorts of failures. For example, I wouldn't have been surprised if power supplies overheated and shut down (or died entirely).

(I think desktop PSUs are often rated as '0C to 50C', but I suspect that neither end of that rating is actually serious, and this was over 50C anyway.)

I rather suspect that running at 50+C for a while has increased the odds of future failures and shortened the lifetime of everything in this machine room (our switches included). But it still amazes me a bit that things didn't fall over and fail, even above 50C.

(When I started writing this entry I thought I could make some fairly confident predictions about the servers keeping running purely from the temperature graph. But the more I think about it, the less I'm sure of that. There are a lot of things that could be going on, including server failures that leave them hung or locked up but still with PSUs running and pumping out heat.)