Comment by cranberryturkey

The parallelism advantage of rclone is real but undersold here. rsync's single-stream design made sense when networks were the bottleneck. Now with high-bandwidth links (especially to cloud storage), the bottleneck is often the round-trip latency of per-file metadata operations.

rclone's multi-threaded transfers effectively pipeline those operations. It's the same principle as why HTTP/2 multiplexing was such a win — you stop paying the latency tax sequentially.

One thing I'd add: for local-to-local or LAN sync, rsync still often wins because the overhead of rclone's abstraction layer isn't worth it when latency is already sub-millisecond. The 4x speedup is really a story about high-latency, high-bandwidth paths where parallelism dominates.