Some of the hardware choices that Backblaze has made in their pod design are interesting. Most of the concerns I have (like the difficulty of getting to drives to replace them) can be addressed by operational practices (update the swift ring rather than immediately replace the drive). Other concerns (like 2gbe for 135TB) are more nuanced. Lack of redundancy in the Backblaze pods is addressed by swift itself--swift will ensure that no two copies are on the same pod.

I would love to see someone run swift on some Backblaze pods. If you'd like to talk further, my contact info is in my profile (or drop by #openstack on freenode).