From my understanding, they've put a lot of work into lowering the cost of storage. I know at one point they were using arrays of consumer-grade drives, and they've done a bunch of analysis on the cost and reliability of drives on the market. They also created the "Storage Pod" [1] to maximize storage density.

[1] https://www.backblaze.com/blog/open-source-data-storage-serv...

Every cloud company does that. Google, Amazon, MS, all use consume-grade drives with software on top to reduce costs and increase reliability at a fraction of traditional enterprise storage solutions. Scality even provides a proprietary solution to do the same on-premise.

Objects on S3 are replicated on 3 AZs (datacenters) by default and I can't find any info on B2 if they also replicate the data on multiple DCs. That can definitely change the cost per GB for them if that's the case.

B2 has 99.999999% durability

That’s nice in theory, but if B2 has a castrophic disaster in thier one data center, that durability goes to zero.

That's just 8 9s. S3 has 11 9s.

Depends upon your client SLA then. You can also store the file twice on B2 for still less than the cost of S3 :)

Will failures be correlated then?

Then you should be comparing it to reduced redundancy S3, which is cheaper than regular S3.

No (no fundamental reason). Yes (same or higher).

Also, AWS costs a lot just in traffic. A lot of people store things on S3 and then make that publicly available.

AWS is "da cloud" for a lot of people. So they ride that wave high and mighty, charging a lot for everything they can easily measure. People will just pay it and will try to [post-]rationalize how it's cheaper than other providers, because AWS is better.

I posted a longer version earlier. But the correct B2 vs S3 comparison is 1 zone infrequent access. B2 still comes out cheaper especially when you consider transfer costs but not by as much.