May i also suggest benchmarking against qfs (the Quantcast FileSystem, formerly kosmosfs)?
https://github.com/quantcast/qfs
It's a high performance native (c++) drop in replacement for hdfs and works extremely well with hadoop. It ships with hdfs java api bindings as well as native bindings for a number of dynamic languages, including python.
One of the main strengths of qfs over the other filesystems you are evaluating is that it makes use of configurable Reed-Solomon encoding to improve the storage-to-fault tolerance relationship while maintaining best of class performance. It also supports appends. With respect to setup, it'svery easy to build and install.