title: ionic externalRootDirectory fails to write to SD card
body: <p>I have been trying without success to write to the (removable) SD card on Android devices using the "cordova-plugin-file" plugin in IONIC.</p>
  
  <p>The documentation specifies the</p>
  
  <pre><code>externalRootDirectory
  </code></pre>
  
  <p>as "Android: the external storage (SD card) root."</p>
  
  <p>However, when I write to this directory:</p>
  
  <pre><code>this.file.resolveDirectoryUrl( this.file.externalRootDirectory)
  .then( (data)=&gt;{
    result += "\n" + "resolveDirectoryUrl";
    newBasePath = data.nativeURL;
    this.file.createDir(newBasePath, newDirName, true)
    .then( ()=&gt;{
      result += "\n" + "createDir";
      this.file.createFile(newBasePath, newFilePath, true)
      .then( ()=&gt;{
        result += "\n" + "createFile";
        this.file.writeFile(newBasePath, newFilePath, this.thisRouteFile,  {append:true})
        .then( () =&gt; {
          result += "\n" + "writeFile OK";
        });
      });
    });
  });
  </code></pre>
  
  <p>the file always gets written to internal memory, or an emulation, not the removable SD card.</p>
  
  <p>There is much discussion of the problem, some citing</p>
  
  <pre><code>  &lt;preference name="AndroidPersistentFileLocation" value="Compatibility" /&gt;
  </code></pre>
  
  <p>but I have found no resolution. </p>
  
  <p>Is it possible to write to a removable SD card?</p>