It's extremely hard to get availability higher than that. Possible but not something companies are willing to promise in an SLA.

I'd say it's not so much that it's really hard, it's that the compromises aren't worth it.

note, I worked on S3 2015-2017

That's a fair point. It would be quite possible if the customers were willing to pay a lot more.

I worked on DigitalOcean's object storage for about a year not long ago. Makes sense that those of us who have been in this space would be interested in this article haha.

So ... e.g. for 5 nines, the erasure code configuration would demand that do more writes in more locations and the cost impact is too high?

I imagine that as you add more nines, you start to hit more problems that are more out of your control. Like, how many nines do your backup diesel generators have?

or replication if you're not erasure coding.

So yeah you need more storage-optimized server racks and all the associated manpower and maintenance, you also need them to be distributed across different datacenters and zones which of course also impacts latency and your ability to provide some appearance of consistency, then you also need the same distribution for stateless services serving the data.

On and on and on and you might be nearly doubling cost to get to an extra 9 that almost all of your customers won't care about.

It's a cost problem. You can absolutely get higher availability, but it requires more hardware, uses more networking, and it makes maintenance and feature development more expensive. Blob storage customers are very price sensitive, but they also want lots of availability. That's why you'll see various "tiers" of storage, to try and capture all the combinations of availability and storage cost that various kinds of customers might want. Pretty much nobody wants to pay twice the cost to turn an exabyte of 99.99% available data to 99.995% available data, so it's not a product.

Absent here is any statement about how available is defined in terms of being _meaningfully up_ like iops or bps.