When running some tests on EC2, I was using mongoperf to evaluate disk performance. mongoperf was run with settings

. Despite ramping up the number of threads (tried up to 64 threads) mongoperf could never do more than ~1100 ops / second. However, if I run multiple mongoperf processes, I was able to get the aggregate up to 5000 ops / second. Seems like 1 mongoperf instance should be able to saturate the disk. I've attached a chart showing iops reported from iostat during the test. the "steps" on the left hand side show the aggregate throughput as i went from 3 -> 4 -> 5 mongo perf instances. the "valleys" are the time during which the new mongoperf is allocating the data file. the bulk of the graph is the performance with 5 mongo perf's running simultaneously.