Generally speaking, the best practice is to have two separate backups, one of them offsite.

First, you might want to run some kind of a RAID setup so that a single disk failure doesn't affect much. RAID is not backup, but it's useful.

Second, you might want to set up some automated backup/copy of your data to a different machine or to a cloud. The advantage is that it's setup-and-forget. The disadvantage is that if you have data corruption or malware, etc. the corrupted data could overwrite your clean backup before you notice something is wrong. Because of that it would not be a bad idea to occasionally make known-clean copies of data (say, after a disk check and a malware check) on some offline media like a flash drive or an external hard drive.

Disk space is really REALLY cheap. It's not rational :-/ to skimp on it.