private int doRun() throws IOException {
    NamenodeProtocol proxy = createNNProtocolProxy();
    NamespaceInfo nsInfo;
    try {
      nsInfo = proxy.versionRequest();
    } catch (IOException ioe) {
      LOG.fatal("Unable to fetch namespace information from active NN at " +
          otherIpcAddr + ": " + ioe.getMessage());
      if (LOG.isDebugEnabled()) {
        LOG.debug("Full exception trace", ioe);