LSFMM: Caching — dm-cache and bcache

Unfortunately I could not attend this session at LSF. But that shall not stop me from plugging a feature of fio that could be useful in testing caching solutions.

When fio is asked to do random IO, the default is for the IO pattern to be uniformly random. That makes it hard to test caching. Fio also has support for using a zipfian [1] or pareto distribution instead, which should provide more real-world like IO patterns.

Set random_distribution=zipf:1.2 for using a zipf distribution with a theta of 1.2. Fio includes a small test app (t/genzipf) that allows you to test and "visualize" distributions with different theta values.

[1] http://en.wikipedia.org/wiki/Zipf%27s_law