How much of that 50 terabytes is media downloaded from the Internet? Because the cheapest way would be to trust that it's already backed up on the Internet and then use one of the usual services like B2 by Backblaze or Storagebox by Hetzner to back the rest of it up.

My suggestion: Buy 3x 28TB drives. Mirror the data to them. Then move them off site.

The off-site location could either be a family member's home where you can then sync to the drives over the internet. Or in a PO box nearby that you retrieve them from time to time to re-sync the data.

Tape is still the cheapest and best archival medium. Drives are expensive, but the actual tape is cheap. But 50TB might not be enough to justify.

In the backup world, 50TB isn't really a lot, and you're not really ready to talk about tape systems or maintaining an always-on disk system. Also, HDD's have been getting more expensive due to AI idiocy. But, cheapest is probably a second raid system, like 4x 20tb drives. Do the backup at home and then move the backup system off site and either keep it spinning, or make sure to spin up and test the individual drives every so often.

Backblaze personal is about the cheapest I know of: $99 per year unlimited. Caveats would be that the drives have to be physically connected to the computer doing the backup. Additionally, should you ever need to restore the backup, the best way would be to buy a 10 tb drive from Backblaze, restore the data, then send the drive back for a full refund x 5. Restoring 50 tb online would be excruciating.

Cold storage solutions would be cheapest if you don't need to access it often, if you do then Backblaze b2.

Lastly you could do your own backup (drives sitting at a friends of family's place?)

First: there is no cheap way to back this amount of data up. AWS Glacier would be about $200/mo, PLUS bandwidth transfer charges, which would be something like $500. R2 would be about $750/mo, no transfer charges. So assume that most companies with some sort of whacky, competing product would be billed by either of these companies with you as a consumer, and you can figure out how this is the baseline of what you'll be getting charged from them.

50TB of what? If it's just readily available stuff you can download again, skip backing that up. Only keep personal effects, and see how much you can reduce this number by.

First thing is decide what data you have that can be readily replaced. e.g. publicly available Linux ISOs. Then remove that from your backup strategy. You may end up with a lot less data needing backup.

Is it data you would trust in the hands of random strangers on the internet? If so, I can easily store 50TB for you, as long as it's temporary.

Oh, and I have various storage solutions in various jurisdictions, so if you have any preferences as to places you do NOT want to store it, that's something you need to hilight.

https://diskprices.com/

is the best resource for finding cheap personal digital storage, last i looked into it not sure how up-to-date that site is kept though

Gee, that's a lot of homework.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

5 acronyms in this thread; the most compressed thread commented on today has 12 acronyms.

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The cheapest medium is tape. It is by far the lowest price per terabyte. The tradeoff is that the drives are pricey, even the used ones, and it's a huge pain to read the data back out (but in a recovery scenario, that's tolerable).

4-bay DAS with a handful of big HDDs in RAIDZ1. Load it up, then store it in your office at work or at a friend or family member's house. Retrieve, update, and scrub somewhere between once every few weeks to once every few months, depending on how often your critical data is changing.

Nobody said this here but storj is one of the cheapest storage out there and it's has redundancy and is distributed. And if you have truenas, it's kinda baked right in. They had some hiccups when communicating changes to the community, but overall nice folks.

Install W11… your data will be backed up…just not the way you want it.