blkreplay is a GPL’ed userspace toolkit, driving the block layer of Linux (or other Unix-like OSes) while measuring latency and throughput of IO operations for later visualization (so-called “sonar diagrams” and others).

In addition to artificial loads like random read-write sweeps and various kinds of overload tests, blkreplay can replay natural loads which have been recorded by blktrace (or Windows DiskMon) at heavily-loaded production servers at big data centers.

Collecting benchmark results is the first step to solving disk I/O performance problems. Unfortunately, many bug reports and performance investigations fall down at the first step because bogus benchmark data is collected. This post explains common mistakes when running disk I/O benchmarks.

To give you a little bit of background when the OSD writes into his journal it uses D_SYNC and O_DIRECT. Writing with O_DIRECT bypasses the Kernel page cache, while D_SYNC ensures that the command won’t return until every single write is complete. So yes, basically the OSD forces all the writes to be flushed prior to start the next IO.

Siege is an http load testing and benchmarking utility. It was designed to let web developers measure their code under duress, to see how it will stand up to load on the internet. Siege supports basic authentication, cookies, HTTP, HTTPS and FTP protocols. It lets its user hit a server with a configurable number of simulated clients. Those clients place the server “under siege.”