title: Synchronize two disks having access to only one of them at a time
body: <p>I need to synchronize two large disks but I can access to them only one by one. So I need to divide the process in two steps:</p>
  
  <ol>
  <li>save (only) the differences from <code>source</code> on the local smaller disk</li>
  <li>apply them to the <code>destination</code>.  </li>
  </ol>
  
  <p>Is it possible to save the current state of <code>destination</code> to a file, to copy on the smaller disk only the differences? With rsync or other tools?  </p>
  
  <p>Something like:</p>
  
  <pre><code># on `destination` disk:  
  rsync &lt;magic option&gt; -o "status_file.delta"  destination/
  
  # `source` to `temporary`:  
  rsync &lt;magic option&gt; -i "status_file.delta" source/ temporary/
  
  # `temporary` to `destination`:  
  rsync -a temporary/ destination/
  </code></pre>
  
  <p>Thanks!</p>