Chris Jepeway recently posted an interesting patch to the NetBSD tech-performance mailing list. His patch provides "disk-level transaction clustering", bunching together a series of contiguous disk read or writes into a single read or write. This logic is added at the disk driver level, after the filesystem has performed its own read-ahead or write-behind logic, providing about a 5% improvement in throughput. Chris says, "None of this is earth-shattering news, of course, but it does demonstrate that clusters can be missed at the FS / VM interface. And that's when only one process uses the disk in question."

I contacted Chris who was kind enough to answer a few questions about his efforts. To learn more, read on...