Nightly? what happens in between and how many different sites? What happens if your Internet goes down one night? How many parity drives do you have? Will the array survive replacing a drive or will another one die during the sync will you lose data if that happens?

S3 takes replication seriously to a professional level, when you upload a file to S3 the chance of s3 losing it is capped by the chance of a civilization killing asteroid hitting the earth.

How often are you testing those backups? What kind of monitoring do you have? Do you pay attention to it? Skip any of those and it's just a prayer.

How much do you pay for offsite backups? How durable are they?