At a previous job I worked on serving data from SSDs. I wasn't really involved in configuring the hardware but I believe they were good quality enterprise-grade

At a previous job I worked on serving data from SSDs. I wasn't really involved in configuring the hardware but I believe they were good quality enterprise-grade SSDs. My experience was that a random read (which could be a small number of underlying reads) from mmap()'ed files from those SSDs took between 100 and 200 microseconds. That's far from your figure of hundreds of milliseconds. Of course 200 microseconds still isn't fast. That translates to serving 5000 requests per second, leaving the CPU almost completely idle. Another odd fact was that we in fact did have to implement our own semaphores and throttling to limit concurrent reads from SSDs.