themachine , 4 hours ago

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.