In an effort to improve repeatability, the MongoDB Performance team set out to reduce noise on several performance test suites run on EC2 instances. After thinking about our assumptions and the experiment setup, we began by recording data about our current setup and found no evidence of particularly good or bad EC2 instances. However, we found that the results of repeated tests had a high variance. Given our test data and our knowledge of the production system, we had observed that many of the noisiest tests did the most IO (being either sensitive to IO latency, or bandwidth). After performing the first baseline tests, we therefore decided to focus on IO performance through testing both AWS instance types and IO configuration on those instances.