code: private void formatJournal(NamespaceInfo nsInfo) throws IOException {
      Preconditions.checkState(nsInfo.getNamespaceID() != 0,
          "can't format with uninitialized namespace info: %s",
          nsInfo.toColonSeparatedString());
      LOG.info("Formatting journal" + this.getJournalId()
          + " with namespace info: (" + nsInfo.toColonSeparatedString() + ")");
      journalStorage.backupDirs();
      journalStorage.format(nsInfo);
      refreshCachedData();
    }
docs: Format the local storage with the given namespace.