> The different media types is probably the hardest issue; I'd wager that for most people, backing up > 2 TB on anything but spinning rust will be impractical/prohibitively expensive.

There's LTO (Linear Tape Open), LTO-8 has 12 TB of raw capacity and costs about 65 - 70 €. The newest variant (not yet _that_ widely available), LTO-9 has 18 TB.

You need a few to handle rotation, but for most that means at max 10 plus one new per year for the long term archive.

We provide Tape support in our open source Proxmox Backup Server product, it can handle single drives and drive robots (with auto exchangers that lessen the work on tape rotation), the data is deduplicated, compressed and optionally encrypted.

https://pbs.proxmox.com/docs/tape-backup.html

PBS can also efficiently mirror to remotes:

https://pbs.proxmox.com/docs/managing-remotes.html

Check the introduction/main feature section for more info if you're interested: https://pbs.proxmox.com/docs/introduction.html