/**
  * Returns the number of bytes used on the harddisk by the file object
  * with the specified object id.
  * @param int object id of a file object.
  */
 function _lookupDiskUsage($a_id)
 {
     require_once 'Modules/MediaCast/classes/class.ilObjMediaCast.php';
     require_once "./Services/News/classes/class.ilNewsItem.php";
     require_once "./Services/MediaObjects/classes/class.ilObjMediaObject.php";
     $obj = new ilObjMediaCast($a_id, false);
     $obj->read();
     $items = $obj->getItemsArray();
     $size = 0;
     foreach ($items as $item) {
         $news_item = new ilNewsItem($item["id"]);
         $news_item->read();
         $mobId = $news_item->getMobId();
         $size += ilUtil::dirsize(ilObjMediaObject::_getDirectory($mobId));
     }
     return $size;
 }