Backing up high volumes what's the best solution

Hey guys,
So I was thinking a way to do an ultra redundant storage machine which will be on RAID 5 with 4 disks of 4 TB. But then I came through the issue of backups how should I manage it simply rebuild another machine with the same spec and in case of a crash the data will be still on the other one?

This seems really inefficient to my eyes, it’s simply a folder to backup which could make up to 12TB. I was thinking of something like duplicati, but yeah…

The thing is that if the two machines are both 12 TB is it still possible to have backups of one week with a lot of compression on the second machine?
What’s your idea?

Go incremental. If data doesn’t change too much you can save space.