[klodolph]

Agreed. The classic reason is when you have latency needs, but your data set is large enough that RAM is cost-prohibitive, and random-access enough that disk won’t work. The cost savings from switching to NVMe have to justify the higher NRE cost, and simultaneously, you have to be sensitive to latency.

[creshal]

Individual NVMe drives are also rather small – the biggest I can find is 30TB, which is still more than what AWS offers me as RAM, but not much. Once you start adding custom algorithms to spread your data over multiple "raw" NVMe drives to get more capacity, the latency gap between your custom solution and existing, well-optimized file system stacks starts to erode. Might as well stick to existing kv stores on ZFS or something, rather than roll your own project that might be able to beat it, maybe.