Re: 600 Servers = 1 truck and lots of muscle
Miners != servers
There are a few different ways of building a rig, which fall into roughly the following categories:
- open air rack, specialist mobo with 8-13 pci-e connectors, 2-3 1600W+ PSUs
- open air rack, high end mobo with 5-7 pci-e connections, 1600W or 2x 100oW PSU
- case + rack, mid mobo with 4-5 pci-e connections, 1000W PSU
- case only, mobo with 2 full size pci-e slots, 800W PSU
The last one look pretty much like a server in a desktop case, I use old Dell Dimensions as the cost per card is cheap, but take up a bit more space. Second last on looks like a server with a rack above it.
To get the density to make paying for a DC worthwhile, you probably need one of the first two arrangements. Since the GPUs are just screwed (or cable tied) into a frame, you can probably pull all the cards in a matter of minutes once you've cut the power. So stripping 600 miners (~3000 cards), 30 seconds a card would be about 17 man hours. So 6 people could probably do it over the course of an night.
"With a powerful enough power supply (with connectors) you can power more than one rig at a time. "
Eh, that's not a good plan. Most PSUs run optimally at about 50% load, so you either overspec the PSU, or you pay a premium for one that will do 80% efficiently and cram lots of stuff on the rig. Using multiple PSUs on a single rig is quite common, but the other way around is not something I've seen, nor would recommend. The GPUs are the big power draw anyway, even an inefficient system will only draw 100-150W at the wall, while each GPU will typically pull an extra 150W (225W for a 1080Ti)*.
"until the market crashes and all you have is a bunch of GPU's which everyone is trying to sell because the currency crashed and there are now a billion cards being sold on ebay"
That's close to what has happened (the crash that is). BTC went to 6k euro, and the alt coins followed suit, now BTC is back at 9k but the alt coins are still priced at the equivalent to 6k. A 1070 or higher is still profitable, my 1060s are just above breaking even, but still being run as a space heater at the moment.
The major use of GPUs is still gaming**. Even cards that are no longer profitable to mine with have considerable resale value. That the prices have been bumped just makes those values higher. A four year old card sells for roughly 30% of it's purchase price, a year old one for 90-110%. Sold my 1060 3Gb cards for about 10-30 euro profit each, plus a years worth of mining.
I've joked that simply buying and reselling GPUs is perhaps even more safe a way to make money than mining cryptos. 10% profit each 6 months, 20% if you buy in bulk.
* YMMV, tuning power versus performance depends a lot on your power price, and how well your particular bit of silicon behaves under low voltage.
** Miners buy about 5% of the GPUs, but are more price sensitive than gamers. Thus the best bang for buck cards get cleared out, the remaining cards get a price bump, and then everyone puts off upgrading. New set of cheap cards arrive, rinse lather repeat.