title: Moving files between volumes in Docker is slow
body: <p>I am mounting two volumes that way:</p>
  <pre class="lang-yaml prettyprint-override"><code>    volumes:
        - /home/username/videos:/var/www/symfony/ftp
        - .docker/data/uploads/videos:/var/www/symfony/public/uploads/videos
  </code></pre>
  <p>Both folders on the host machine are on the same partition. If I run <code>mv</code> on the host for files between <code>/home/username/videos</code> and <code>.docker/data/uploads/videos</code>, it's basically instant. But if I run <code>mv</code> between <code>var/www/symfony/ftp</code> and <code>/var/www/symfony/public/uploads/videos</code>, it's painfully slow.</p>
  <p>Basically, it seems like it's copying the file as if it was two completely different physical drives. The host machine is running Ubuntu 20.04, the Docker image Alpine 3.13.</p>
  <p>Is this behavior expected? Any idea how I could improve that, if possible? (Other than just having both folder on the same volume)</p>