This is highly dependent on the filesystem - as far as I know, basically only XFS works, and only for a small subset of operations, and everything else just blocks.

Tokio's filesystem handling in Rust is the same way by default - a pool of IO threads.

Edit: I just remembered that Avi Kivity (of KVM and ScyllaDB fame) wrote a tool to detect this: https://github.com/avikivity/fsqual