Your title is about backups but your question seems mostly just about how to set up your storage for backups.
You can go about pooling disks in a few ways but you first need to define what level of protection from failure you want. Before going further though, how much space do you project that you will need for backups?
If you want simple you’ll have to manually decrypt each time it needs doing.
If you want it to be “automatic” then your best bet is something network based. A “simple” would be to just have a script ssh’s somewhere, pulls the decryption key, and then decrypts the disks. There’s plenty of flaws with this though as while a threat actor couldn’t swipe a single encrypted disk they could just log in as root, get your script, and pull the decryption key themselves.
The optimal solution would be to also encrypt the root partition but now you need to do network based decryption at boot which adds further complexity. I’ve previously used Clevis and Tang to do this.
I personally don’tencrypt my server root and only encrypt my data disks. Then ssh in on a reboot or power event and manually decrypt. It is the simplest and most secure option.
I backed this: https://www.crowdsupply.com/cool-tech-zone/tangara
Its not yet released and is in the manufacturing process but I think it’s worth considering
They watch the swarm. You can view connections of the swarm. They see your ISP owned IP and send an email.
I prefer restic for my backups. There’s nothing inherently wrong with just making a copy if that is sufficient for you though. Restic will create small point in time snapshots as compared to just a file copy so I’m the event that perhaps you made a mistake and accidentally deleted something from the “live” copy and managed to propagate that to your backup it is a nonissue as you could simply restore from a previous snapshot.
These snapshots can also be compressed and deduplicated making them extremely space efficient.
Assuming the implementation is done in such a way that I am not indirectly owned by the manufacturer of the BCI and am capable of maintaining its software and firmware myself…yes yes absolutely yes stick that shit in my head.
But if it is not open source and I’m expected to be tied to some corporate entity just to utililze it, no, absolutely not.
Trust no one. Not fully at least.
Just look at the bit rate of what you are streaming and multiply it by 3 then add a little extra for overhead.
If the total data is 3tb and you want disk failure protection I would take your two 6tb disks and put them in a mirror. With the amount of data you have and the drive sizes at your disposal that makes the most sense. This leaves you with 3tb free for growth. If you wanted an additional backup I would recommend storing it in a different location entirely or pay a cloud provider like Backblaze.
I would do this with ZFS but you can also do this via LVM or just straight md-raid/mdadm. I’m not sure what your issues are with zfs on popos but they should be resolvable as Ubuntu supports zfs fine to my knowledge.
An alternative you could consider is using mergersfs to logically pool indivial filesystems on each of the disks and then use SnapRAID to provider some level of protection. You’ll have to look into that further if interests you as I don’t have to much info in my head related to that solution. Its not as safe as a mirror but its better than nothing.