I have a Pi3, running Raspbian, with installed free software "UrBackup" https://www.urbackup.org/ Attached to that Pi3 is a 4Tb Western Digital Red Plus drive in an external enclosure.

The UrBackup server runs on the Pi3, and the UrBackup clients run on each of our home computers that I am backing up.

Each computer is backed up once each day, in the middle of the night. I do file backups on both Linux computers and Windows computers, and additionally do image backups on the Windows computers. I have half a dozen or so computers that are backed up with this system. The 4Tb drive is large enough to hold one years worth of daily file backups for each computer, and the monthly image backups from the Windows computers. UrBackup takes care of cleaning up old backups that are past 365 days old. Obviously, you configure how frequently to do backups and how long to keep them. My personal choice was daily/365 days.
UrBackup is smart enough that if I add a large computer to the backup mix, so that the current 4Tb drive is not big enough, UrBackup would make the decision that "Hey, I don't have room for a years worth of backups anymore, so I'll delete the oldest ones to make room for the newer ones".

UrBackup is totally free, and has a nice webserver interface for setup/maintenance. The biggest thing for me is that UrBackup does not use any proprietary formats and you could just pull it's backup data disk and install that into another computer and restore your files from there without even needing the UrBackup software. Of course you'd have to do a little detective work to learn the file structure that UrBackup uses, but that's easy. Using UrBackup for restores is certainly easier, but it's nice to know that it is not absolutely required.

UrBackup does not store multiple copies of a file if it's not changing, it uses symlinks in the background to make an older but unmodified file version appear to be in a newer backup. And it also does this symlinking for files from multiple different computers. Say you have "filename" existing on three separate computers, all identical. UrBackup will save one copy of this file and then symlink that to the other computers backups. This is why it's so efficient on disk space and I can hold one year of daily backups from half a dozen computers on one 4Tb disk. Once you look at your backup disk and see, "Ah, this is how UrBackup does this!" then you are free to restore from backup in any way you wish - not requiring UrBackup if that is what you desire.

If you decide to set this up on a Pi, I would recommend a Pi4 over a Pi3. The Pi3 has the horsepower to run UrBackup, BUT the Pi3 only has USB2, the Pi4 has USB3. That makes for MUCH faster disk reading/writing. If you're like me and do your backups in the middle of the night when you're sleeping and don't care how long they take, a Pi3 works fine. But get the Pi4 anyway - I think you'll be happier in the end.

One other thing - for reliability, I do not have my Pi3 boot and run off the microSD card. I changed the bootloader so it loads the OS from the 4TB harddisk and runs from there. So I don't have to worry about the problem that some people encounter of a corrupted microSD card in the Pi3.