> I'd have first deployed existing, native code along with
> Rust in parallel using the data splitting technique so
> some is saved with original and some with Rust.
Yes, this is how Dropbox tests all of their features, and they did this with their new Rust-based storage engine as well. This tool has been in development for over a year by now and has seen extensive multi-stage testing (at first handling only a few terabytes of data, then "just" petabytes, and now exabytes).