For one, this has no redundancy and doesn't factor the cost of the machine providing the storage. But also it's an upfront cost for storing 4TB. It would be implied you wouldn't literally store 4TB on the SSD because now you're out of capacity for more data. If you only have 2GB of data in a bucket then S3 is still magnitudes cheaper, faster, and more redundant than anything you could put together yourself because the cost is spread across all the users of the service.

Reality is there are so many times that S3 makes the most sense that it makes people short-circuit and always pick S3 despite the huge hidden IOPS and bandwidth costs everyone rightfully tries to point out.

This is badly misunderstanding the problem: S3 is a highly available service with geographic redundancy and a huge range of integrated features. Your comparison would need to be updated to include multiple running servers in addition to redundant storage, and the software stack implementing things like immutability, not to mention all of the security features.

That’s not to say that you can’t build equivalents for the parts you use but you either need massive scale or giving up features to do that. For example, if you can tolerate bitrot or long access times if hardware fails, you can definitely get a lower cost per terabyte.

The reason why most people don’t do that, even when they have scale, is that it adds cost and risk everywhere else if you need engineering/ops people working on storage. If you’re, say, the internet archive that might make sense—it’s quite literally why your organization exists—but most other places are going to see all of the integrated features that they don’t have to build and operate paying for the difference between S3 and physical media pricing. For example, if I want to process files as soon as they’re uploaded or have immutability, I can just turn that on rather than having to build more services.

- Directory entries are no longer returned in sorted order in ListObjectsV2

- There's an AppendObject API

- There's a RenameObject API