[pkolaczk]

Technically correct, but filesystems are mostly about I/O. For example this Baidu filesystem copies blocks of data into userland memory and transfers them in RPC messages - any system using proper zero copy approach would easily beat it even if coded in Python or JS. Baidu also seems to use threads, locks and SEDA instead of more efficient (but much harder to code) thread-per-core async architecture. Threadpools and lock based synchronization are terrible for latency.

The fact that something is in C++ doesn't make it automatically efficient. And particularly, if we're talking about milliseconds, not nanoseconds here, in Java or C# you can do just everything what you can do in C++, performance-wise.