Internal measurements have indicated to us that, in our loading pattern, the qmail queue sustains roughly 10 times as much write activity as the end-user mailboxes, which in turn sustain roughly 10 times as much write activity as the logs. The first factor is of primary importance. It will vary depending on the ratio of queued messages to local deliveries -- the more local deliveries, the lower this number will be. However, since maildir delivery requires fewer synchronous writes than the inject/process/clean qmail process, the ratio will always be significantly more than 1. Therefore, the qmail queue will always be the primary bottleneck to performance (when considering only the filesystems).
The goals of this set of benchmarks are to determine which of the commonly used Linux filesystems (in particular, ext2, ext3, and ReiserFS) offer the best performance when used with qmail.