It's addressed in the section "A Backblaze Storage Pod is a Building Block"

From the article:

When you run a datacenter with thousands of hard drives, CPUs, motherboards, and power supplies, you are going to have hardware failures it’s irrefutable. Backblaze Storage Pods are building blocks upon which a larger system can be organized that doesn’t allow for a single point of failure.

Sounds to me like they haven't implemented this yet. I wouldn't want my data on that sort of solution. Backed up data would surely need a level of geographic redundancy.

In the next section they say they have implemented the machine level redundancy. As for geographic redundancy I think the idea is that you use them for that. As in you backup your data locally and then send it to them as a redundant copy.

It is called a fuse.

To get all the various logos and certifications on them, they are required not to do that. Every line is voltage limited.