protected function extract($serial)
    {
        $serial = $this->cleanSerial($serial);
        $parts = explode('/', substr($serial, strpos($serial, '://') + 3), 2);
        if (count($parts) != 2) {
            throw new FileSerializerException('Unsupported dir in '.__CLASS__);
        }

        return ['fs' => $parts[0], 'path' => $parts[1]];
    }