private function removeFolderInFileSystem(Folder $folder)
	{
		$folderPath = $folder->getPath(DIRECTORY_SEPARATOR, true);

		$folderExternalPath = $this->getExternalPath() . $folderPath;
		$folderInternalPath = $this->getInternalPath() . $folderPath;

		//remove empty _size folders (or whatever the prefix is); we expect these folders to be empty
		foreach (array($folderExternalPath, $folderInternalPath) as $path) {
			$sizeBase = $path . DIRECTORY_SEPARATOR . self::RESERVED_DIR_SIZE;
			if (is_dir($sizeBase)) {
				foreach (glob($sizeBase . DIRECTORY_SEPARATOR . '*') as $subSize) {
					@rmdir($subSize);
				}
				@rmdir($sizeBase);
			}
		}

		// we are ignoring that one of the folders might not exist
		$resultInternal = @rmdir($folderInternalPath);
		$resultExternal = @rmdir($folderExternalPath);
	}