Trader Joe’s has a completely mirrored datacenter in a different geographic location.
I don’t know how they handle data replication but they evidently understand the importance of redundancy.
That mirroring stuff is designed with the idea that one data center will lose power or be destroyed by terrorists.
However, if the database becomes corrupt, and you are using physical mirroring, you now have two copies of a corrupt database in two data centers. And we have found that bugs in the software are far more likely to happen than losing a data center.