Now there is a period when large companies are decommissioning 2017-2019 hard drives, volumes are already over 10 TB there, and it is possible to build reliable arrays of the RAID60 level with a volume of hundreds of terabytes.
Some Vendor-locked models like HGST, which are not flashed, do not cost anything at all. I have already written - the cost of data storage is well, if not zero, then very low, far from $ 1 per Tb. Now you can buy used hard drives at a price of $ 5-7 per terabyte, those who sell them buy “by weight”, “tons”, “vans”. They generally have an incoming price of about 0.
And if you build an array on old 1-TB disks that people just throw away without even trying to sell, and you collect 200-300 pieces of them, then you will have a free array at all. It remains only to put it in a place with free electricity, and there are plenty of such places!
Before the Chia mining boom, a decommissioned 24-disk LFF shelf cost about $ 50 per purchase, at the entrance about $ 10. A good cable cost more than a disk shelf with two expanders and two power supplies.
Yes, it is possible without disk shelves at all, as with Chia miners - just connect hard drives directly to the controller (LSI 9264 costs about $ 20 together with BBU), plug 4-5 such controllers into the server, or connect 100-200 disks to one server through an expander ($30). Hobby is one thing, industrial token mining is another.
It’s one thing when a company needs to show business growth - for investors or journalists, and quite another thing when a company needs to make money. We were in the first phase, now we are moving into the second, and we must be aware that if you do not know how to save money, if you have expensive electricity, there is no way to buy old decommissioned hard drives, then most likely you will be left behind.