Earlier quoted context omitted.
Latency ought to be much better, since you're skipping several abstraction layers in the kernel. But that's about it. And the latency is still worse than in-memory solutions. Between that and the non-trivial effort needed to make this work in any sort of cloud setup (be it self-hosted k8s or AWS), it's a hard sell. If I really need latency above all, AWS gives me instances with 24TB RAM, and if I don't… why not just…
While you can get 24TB ram, there is a pretty big cost difference. 2 TB of ram costs roughly $10000 compared to $130 for NVME storage (or $230 for 12 TB of a good hard drive). Sure the NVME is ~3.5x more expensive, but the latency will be dramatically lower and the throughput will be dramatically higher. Sure you can build a 24 TB ram system, but at that point the cost of the server will be entirely the ram. The reas…
But when your latency requirements are so tight that you cannot possibly afford the latency penalty of a filesystem, you better have a good business case to justify either developing a custom bare-metal-nvme (which is $$$$$ and takes time) or getting a multi-TB RAM system, which is also $$$$$, but far more predictable, and can be put into production today, not 6+ months later when you finish developing your custom kv store.
For the other 99.999% of use cases, sure, just go with NVMe backing your regular virtualization/containerization infrastructure.