AFAIK Dropbox team was one of the first adopters of Go and Rust languages. Considering their infrastructure requirements it looks reasonable. Dropbox has to fight for each RAM byte and CPU tick because this is the only way to provide high speed and low latency access to your images of cats, tits and whatever UHD porn videos you have stored in cloud.

You can read full story about how Rust will improve your file storing experience following next link Rewriting the heart of our sync engine.