cp is single-threaded and only blocks on one IOP at a time. With a tarpipe, you can block on two IOPs at a time, and they're decoupled by the pipe buffer. Thi

cp is single-threaded and only blocks on one IOP at a time. With a tarpipe, you can block on two IOPs at a time, and they're decoupled by the pipe buffer. This primarily makes a difference because the kernel cannot issue the I/O for small files ahead of time, like it does when you sequentially read a large file, so you do actually end up blocking and waiting.