Best way is to backup using tapes, which few organizations do in the age of the cloud.
Is that still a thing? Why would a tape be better than ...oh, any other format?
Yes tapes are still a thing because they are the cheapest per GB at $0.01/GB and have lower error rates than drives and generally last longer.
http://www.overlandstorage.com/blog/?p=323Main reason is some tapes cannot be overwritten, so its not possible for ransomware to encrypt your backups. That happens quite a lot
http://www.sbsfaq.com/?p=4046