Let me suggest the Quantcast File System (QFS) [0]. It's much closer to GFS as described in the paper (crucially it uses Reed-Solomon encoding to reduce storage requirements), it's highly tunable to different workloads, and it's written in C++. Quantcast uses it to store petabytes of data and for running map reduce. Unfortunately it hasn't seen much uptake outside of Quantcast, despite being a clear improvement over HDFS.

[0] http://quantcast.github.io/qfs/

(Disclaimer: I used to work for Quantcast).