Many people who have home servers (me included) buy used enterprise gear for this reason.
Pitfalls: Server-class hardware can take a very long time to POST, as they're intended to run 24x7, and (especially 1U and 2U boxes) tend to have extremely loud fans.
If you want a quiet server, your best bet is to build it up from a server motherboard and a 4U case, and use quiet fans like Noctua.
Consumer-class hardware is more often built with the assumption that it's going to get thrown in an all-glass case starved of airflow, so they put heatsinks everywhere and expect specific air pathways in a standard atx case.
You're probably fine to go either way really, but the hardware is probably going to have a lower lifetime by going for slower airflow.
If you are concerned about noise, do not buy a 1U unit. Small fans still need to move air. Since they are small the way to make up for this is to have a lot of them and make them spin very fast. The faster they spin the more noise they make.
Not even close for new, but a generation or two old can be had very cheaply.
I was was once gifted a 128 node cluster (with the racks, UPS, everything) to a lab for the tax write off alone - they even provided shipping. The servers were only 3 years old iirc, but had depreciated enough on their books I guess and they wanted a faster cluster.
I recall as college students finding a VAX 780 on the "getting rid of it" part of the engineering loading dock and we got permission to get rid of it for them. Pushing it down the street at 11pm was interesting (getting a weird look from a police car going by).
It got gutted for parts (power supplies don't care too much about what they power) and converted into a lockable bookshelf and 14" diameter wall hangings (and some surprisingly strong magnets).
The "yea, we let a bunch of college students take it" was a significant savings over getting a truck to haul it off to some junkyard even before the days of being very picky about electronics recycling.
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http://www.reddit.com/r/homelab/
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Good luck! Rackmount machines are their own world. Done right they last longer than desktops with the added benefit of typically being quite loud. Stay cool. B-)
I'm a gamer and upgrade my primary gaming machine on a much tighter cycle than a lot of other people, which means I have a fair bit of hand-me-down hardware around to pass along. Sometimes, instead of just selling/trading/giving my old stuff away, I'll stick the consumer-grade stuff inside my 4U rack boxes.
Basically, it comes down to customizability and the space to do what I want in it.
For example, my NAS server's case has 18 drive bays. With modern motherboards supporting NVMe, it's very doable to run the OS off NVMe, a couple of caching SSDs and an array that is 20TB+ large, and bonded 2.5GBe (maybe upgrading to 10 someday) to my VM Host machine. Most out of the box NAS systems don't do that.
My other server I use for hosting VMs and cracking hashes (not crypto, think password cracking) and has a few older GPUs in it to accelerate that task.
Nowadays a lot of consumer-grade CPUs have as many or more cores than older second hand server equipment, and often can run lower power (not always true). Plus putting it into 4U boxes means I can more larger fans so it's quieter than traditional aircraft-engine servers.
This is by some people's definition "doing it wrong" because I don't have ECC memory, etc., but the reality is I've been running it for years now and it's been very stable, with only one hardware failure over the course of the decade or so I've had this system together.
So you use consumer CPUs in rackmount hardware? Are you able to use any consumer PC components in a rackmount rig? I'd love to build a home server and I can see the benefit to better ventilation/noise result with rackmount, and I imagine rackmount uses the same hard drives, but are other PC parts equally usable?
For networking gear, it can be nice to have a small rack, but very much not necessary.
It isnt about the "form factor" - but the cost. Businesses buy rackmount servers because it is space-efficient.
Eventually they sell these off very cheap and unlike your desktop grade equipment business servers are built to last. while that 5 year old business server may be out of date for them, they still have plenty of life left and can be had for dirt cheap.
i have a multimedia server in my basement with 72GB ram and dual Xeon's which i picked up for around the cost of a decent desktop motherboard.
So in short. Rackmount equipment purchased brand new is very expensive, but buying old "end-of-life" gear is very cheap. The depreciation on computer equipment would put a car to shame.
However, rack equipment will always cost more than non-rack equipment because rack equipment isn't targeted for consumers. An APC UPS that fits in a rack is $500, when the equivalent standalone one is $150.
Noise is another downside to rack equipment: It's designed to run in rooms with massive air conditioners, so the noise floor they're trying to stay under is "sports stadium".
There often aren't actual equivalents available in consumer, so it's hard to get an apples-to-apples comparison. Which isn't to say a consumer grade piece of kit won't be fine for your use, just that you aren't paying $500 vs $150 for "the same thing", rather the $500 one has a bunch of feature and/or component quality stuff you may not care about (and some extra margin, but nothing like 200% you suggest)
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