My box has 16 TB of ECC RAM for 25 TB+ worth of nodes. The RAM was cheap, I got old used chips for almost pennies, IIRC I’ve spend half of a single month of Storj revenue. Good investment too, it made a huge change to win ratio and profit.
I wish I could fit more RAM, but this box won’t accept, CPU’s too old.
BTW, storage nodes could be optimized more regarding memory use. I don’t know how much RAM is needed by NTFS, but for default ext4 setups 1 GB of RAM can hold metadata of 1 TB worth of nodes. Optimized ext4 can go as low as 500 MB of RAM per 1 TB worth of nodes. I’ve got some back-of-a-napkin estimate that it should be possible to write code so that only 200 MB of RAM would be necessary per 1 TB of nodes, regardless of the underlying file system. It’s a lot of work, though, it’s easier to just get more RAM or SSD for caching.