Backing Up Data to Third Offline Copy

We have VxRail and Data Domains but are investigating what to do about an air-gapped or offline copy.  What are you doing about ransomware threats and do you copy to the cloud, tape or a third Data Domain?   The data set we are looking at is either 100TB or 300TB.   I would think the 300TB would be the data set we would use.  There are concerns if you backup to the cloud, you still have a connection that could be compromised via network and ransomware. 

• What best practices are places using to create a third copy if they use VxRail and Data Domain?
• If you want to use the cloud, how do you copy it to the cloud given bandwidth? 
• If you want to export to tape, you have to use ADMe to export to a staging area first.  Is this the best option? 
• What technical steps have you taken to ensure a third copy is saved?

I am not technical in VxRail, so I would appreciate suggestions that places have taken.   Thank you.