Who said anything about low latency? The thing you get from a simulated block device is predictable, controllable latency. Latency that can be deterministically

Who said anything about low latency? The thing you get from a simulated block device is predictable, controllable latency. Latency that can be deterministically replayed. Latency that can be precisely normalized away in the benchmark results, without worrying about inter-batch anomalies (if using separate disks) or the effects of wear (on the same disk.)