Sukru,
that 6TB will definitely be based upon, years of repeated automated backups - adjust your automatic backups and keep 1 copy - give a few days before moodle deletes older copies overtime, you'll likely be left with 1/4th of that size
rest for database, go into database and sort tables by size, on top most probably will be standard log, just empty that database and again you'll be left with much smaller size.
that 6TB will definitely be based upon, years of repeated automated backups - adjust your automatic backups and keep 1 copy - give a few days before moodle deletes older copies overtime, you'll likely be left with 1/4th of that size
rest for database, go into database and sort tables by size, on top most probably will be standard log, just empty that database and again you'll be left with much smaller size.