[traceroute66]

Everyone here has been jumping in and saying "use my great service" or "use this great service".

But could I be the voice of reason here and jump in and remind the OP and everyone else to avoid putting all their eggs in one basket.

Even if you can't afford to replicate 6TB on multiple services, you should at the very least seriously consider picking, say three hosting services (preferably in different jurisdictions) and putting 2TB in each one.

In terms of offline/non-live backup itself, 6TB is really not that much these days. You could just buy a bunch of high-capacity hard drives, create multiple copies and spread them out via old-school "sneakernet" to your collaborators in different jurisdictions. Sometimes KISS is the best solution.