This is a price question mostly. I'm paying $100/yr for the lower end iDrive Personal plan. I'm using about 1.25 TB, and it's growing at a rate of a few GB a year at this point (for the past 4 or 5 years). It's mostly for archival uses (photos, short 60 second movies, and compressed music files). In the past year I haven't even updated what's online, probably haven't logged in either, but it's important to know that the files are safe.
I used to use amazon glacier with the FastGlacier client, but it didn't feel like a good solution for someone who only touched these files once or twice a year.
I feel like I'll want to maintain these archives for another 20-30 years, and at that point I'll be too old or feeble to care. Should I keep sucking up $100/yr, or is there another alternative, like a local cold storage solution (for very little disk space) that might be a 1 time cost, then it just works. What getting a synology type box and turning it on once a year (kinda like starting up that generator you keep in your garage).