Comment by jmb99 | Hacker News Reader

Comment by jmb99 | Hacker News Reader

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Fairly frequently, 6kVA UPSs come up for sale locally to me, for dirt cheap (<$400). Yes, they're used, and yes, they'll need ~$500 worth of batteries immediately, but they will run a "normal" homelab for multiple hours. Mine will keep my 2.5kW rack running for at least 15 minutes - if your load is more like 250W (much more "normal" imo) that'll translate to around 2 hours of runtime.

Is it perfect? No, but it's more than enough to cover most brief outages, and also more than enough to allow you to shut down everything you're running gracefully, after you used it for a couple hours.

Major caveat, you'll need a 240V supply, and these guys are 6U, so not exactly tiny. If you're willing to spend a bit more money though, a smaller UPS with external battery packs is the easy plug-and-play option.

> How bottomless of a pit it becomes depends on a lot of things. It CAN become a bottomless pit if you need perfect uptime.

At the end of the day, it's very hard to argue you need perfect uptime in an extended outage (and I say this as someone with a 10kW generator and said 6kVA UPS). I need power to run my sump pumps, but that's about it - if power's been out for 12-18 hours, you better believe I'm shutting down the rack, because it's costing me a crap ton of money to keep running on fossil fuels. And in the two instances of extended power outages I've dealt with, I haven't missed it - believe it or not, there's usually more important things to worry about than your Nextcloud uptime when your power's been out for 48 hours. Like "huh, that ice-covered tree limb is really starting to get close to my roof."

This is a great example of how the homelab bottomless pit becomes normalized.

Rewiring the house for 240V supply and spending $400+500 to refurbish a second-hand UPS to keep the 2500W rack running for 15 minutes?

And then there's the electricity costs of running a 2.5kW load, and then cooling costs associated with getting that much heat out of the house constantly. That's like a space heater and a half running constantly.

Late reply I know, but I wanted to clear up that I don’t want to normalize a 2.5kW homelab. Usually when talking to people about it I refer to it as “insane.” But, having an absolutely insane amount of computer and RAM is fun (and I personally find it genuinely useful for learning, in particular in terms of engineering for massive concurrency) and I can afford the hydro, so whatever. To match the raw compute and RAM with current gen hardware, you only need maybe 500W - you’ll just be spending a shitload of money up front, instead of over time on hydro. (To match my current lab’s utilized performance, I’d need at least 2 servers, one of which with a ~threadripper 7955WX and 256GB of DDR5, and another with an Epyc 9475F and 1TB of DDR5. That would put me somewhere in the neighborhood of $35k? Ish? Costs me about $115/month to run the rack right now (cheaper than my hot tub) and cooling is free in the winter (6~7 months of the year) so the break even is loooooong term. And realistically, $100ish a month isn’t crazy, considering I self host basically everything - the only services I pay for are my VPS to run my mail server, and AWS for glacier S3 for backup-of-last-resort.

Again, not trying to normalize 2500W, most people don’t need that (and I don’t really either), but I do make good use of it.

As for “rewiring the house for 240V”, every house* in Canada and the US is delivered “split-phase” 240V (i.e. 240V with a centre tapped neutral, providing 120V between either end of the 240V phase and neutral or 240V from phase to phase), and many appliances are 240V (dryers, water heaters, stove/ranges/ovens, air conditioners). If you have a space free in your breaker panel, adding a 240V 30A circuit should cost less than $1k if you pay an electrician, and can be DIY’d for like $150 max unless you have an ancient panel that requires rare/specialty breakers or the run is very long. It’s far from the most expensive part of a homelab unless you’re running literally just a raspberry pi or something.

*barring an incredibly small exceptional percentage

I agree with you. My use case doesn't call for perfect uptime. Sounds like yours doesn't either (though you've got a pretty deep pit yourself, if 240v and generator weren't part of the sump plans and the rack just got to ride along (that's how it worked for me)).

But that doesn't mean its for us to say that someone else's use case is wrong. Some people self host a nextcloud instance and offer access to it to friends and family. What if someone else is hosting something important on there and my power is out? My concerns are elsewhere, but there's might not be.

My point was simply that different people have different use cases and different needs, and it definitely can become a bottomless pit if you let it.

For me, IPMI, PiKVM, TinyPilot, any sort of remote management interface that can power on/off a device and be auto powered on when power is available, so you can reasonably always access it, and having THAT on the UPS means that you can power down the compute remotely, and also power back up remotely. Means you never have to send someone to reboot your rack while youre out of town, you dont shred your UPS battery in minutes by having the server auto boot when power is available. Eliminates reliance on other people while youre not home :tada:

But again, not quite a bottomless pit, but there are constant layers of complexity if you want to get it right.

> though you've got a pretty deep pit yourself, if 240v and generator weren't part of the sump plans and the rack just got to ride along (that's how it worked for me)

Generator was a requirement for the sump pump. My house was basically built on a swamp, so an hour in spring without it means water in the basement. Now admittedly, I spent an extra couple hundred bucks to get a 240V generator with higher capacity than strictly necessary, but it was also roughly the minimum amount of money to spend to get one that can run on gasoline or propane, which was a requirement for me. 240V to the rack cost me $45, most of that cost being the breaker (rack is right next to the panel).

> What if someone else is hosting something important on there and my power is out? My concerns are elsewhere, but there's might not be.

I host roughly a dozen services that have around 25 users at the moment, but I charge $0 for them. I make it very clear: I have a petabyte of storage and oodles of compute, feel free to use your slice, and I’ll do my best to keep everything up and available - for my own sake (and I’ve maintained over 3 nines for 8 years!). But you as a user get no guarantee of uptime or availability, ever, and while I try very hard to backup important data (onsite, offsite split to multiple locations, and AWS S3 glacier), if I lose your data, sucks to suck. So far most people are pretty happy with this arrangement.

I couldn’t possibly fathom worrying about other people’s access to my homelab during a power outage. If I wanted to care, I’d charge for access, and I’d have a standby generator, multiple WANs, a more resilient remote KVM setup, etc. But then I’d be running a business - just a really shitty one that takes tons of my time and makes me little money. And is very illegal (for some of the services I make available, at least), instead of only slightly illegal.

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