«WE HAVE MIRRORED DATA CENTERS, THAT'S WHY WE DON'T NEED BACKUP!»

Mirrored data structures are important and good for ensuring application availability. If you are attacked by ransomware, mirroring works exactly as it should: it ensures that the data is encrypted on both sides.
To protect your data against encryption trojans, the only thing that helps is a backup with many versions that can no longer be changed.