title: Rsync previous half-copied files?
body: <p>I found <code>rsync</code> behaves differently in the following two situations:</p>
  
  <p>(1) All the files are copied by using <code>rsync</code>, then using <code>rsync</code> again will be fast (skip all the files);</p>
  
  <p>(2) Use <code>cp</code> to copy files, then using rsync will be slow (or may be run freshly?)</p>
  
  <p>So my confusion is "Does <code>rsync</code> generate any internal things on the files so that it can refer to avoid duplicate checking?"</p>