BorgBackup creates compressed and de-duplicated backups, splitting data into chunks then only keeping unique chunks + a list of files those chunks belong too.
I've currently got around 470gb being backed up; compression brings that down to 320gb, then after de-duplication that's down closer to 70gb. (there's a lot of media metadata in there, results will vary)
17 backups going back 6 months: 8.10 TB original > 5.62 TB compressed > 326.55 GB final backup data stored on disk
/edit this thread is a week old.... It showed up at the top of my 'new' feed...? Odd.