/**
   * Get the rootdir.  Make sure its wholesome and exists before returning.
   * @param rd
   * @param conf
   * @param fs
   * @return hbase.rootdir (after checks for existence and bootstrapping if
   * needed populating the directory with necessary bootup files).
   * @throws IOException
   */
  private Path checkRootDir(final Path rd, final Configuration c,
    final FileSystem fs)
  throws IOException {
    // If FS is in safe mode wait till out of it.
    FSUtils.waitOnSafeMode(c, c.getInt(HConstants.THREAD_WAKE_FREQUENCY,
        10 * 1000));
    // Filesystem is good. Go ahead and check for hbase.rootdir.
    try {
      if (!fs.exists(rd)) {
        fs.mkdirs(rd);
        // DFS leaves safe mode with 0 DNs when there are 0 blocks.
        // We used to handle this by checking the current DN count and waiting until
        // it is nonzero. With security, the check for datanode count doesn't work --
        // it is a privileged op. So instead we adopt the strategy of the jobtracker
        // and simply retry file creation during bootstrap indefinitely. As soon as
        // there is one datanode it will succeed. Permission problems should have
        // already been caught by mkdirs above.
        FSUtils.setVersion(fs, rd, c.getInt(HConstants.THREAD_WAKE_FREQUENCY,
          10 * 1000), c.getInt(HConstants.VERSION_FILE_WRITE_ATTEMPTS,
        		  HConstants.DEFAULT_VERSION_FILE_WRITE_ATTEMPTS));
      } else {
        if (!fs.isDirectory(rd)) {
          throw new IllegalArgumentException(rd.toString() + " is not a directory");
        }
        // as above
        FSUtils.checkVersion(fs, rd, true, c.getInt(HConstants.THREAD_WAKE_FREQUENCY,
          10 * 1000), c.getInt(HConstants.VERSION_FILE_WRITE_ATTEMPTS,
        		  HConstants.DEFAULT_VERSION_FILE_WRITE_ATTEMPTS));
      }
    } catch (IllegalArgumentException iae) {
      LOG.fatal("Please fix invalid configuration for "
        + HConstants.HBASE_DIR + " " + rd.toString(), iae);
      throw iae;
    }
    // Make sure cluster ID exists
    if (!FSUtils.checkClusterIdExists(fs, rd, c.getInt(
        HConstants.THREAD_WAKE_FREQUENCY, 10 * 1000))) {
      FSUtils.setClusterId(fs, rd, UUID.randomUUID().toString(), c.getInt(
          HConstants.THREAD_WAKE_FREQUENCY, 10 * 1000));
    }
    clusterId = FSUtils.getClusterId(fs, rd);

    // Make sure the root region directory exists!
    if (!FSUtils.rootRegionExists(fs, rd)) {
      bootstrap(rd, c);
    }
    createRootTableInfo(rd);
    return rd;
  }
  public void splitLog(final List<ServerName> serverNames) throws IOException {
    long splitTime = 0, splitLogSize = 0;
    List<Path> logDirs = new ArrayList<Path>();
    for(ServerName serverName: serverNames){
      Path logDir = new Path(this.rootdir,
        HLog.getHLogDirectoryName(serverName.toString()));
      Path splitDir = logDir.suffix(HLog.SPLITTING_EXT);
      // rename the directory so a rogue RS doesn't create more HLogs
      if (fs.exists(logDir)) {
        if (!this.fs.rename(logDir, splitDir)) {
          throw new IOException("Failed fs.rename for log split: " + logDir);
        }
        logDir = splitDir;
        LOG.debug("Renamed region directory: " + splitDir);
      } else if (!fs.exists(splitDir)) {
        LOG.info("Log dir for server " + serverName + " does not exist");
        continue;
      }
      logDirs.add(splitDir);
    }

    if (logDirs.isEmpty()) {
      LOG.info("No logs to split");
      return;
    }

    if (distributedLogSplitting) {
      splitLogManager.handleDeadWorkers(serverNames);
      splitTime = EnvironmentEdgeManager.currentTimeMillis();
      splitLogSize = splitLogManager.splitLogDistributed(logDirs);
      splitTime = EnvironmentEdgeManager.currentTimeMillis() - splitTime;
    } else {
      for(Path logDir: logDirs){
        // splitLogLock ensures that dead region servers' logs are processed
        // one at a time
        this.splitLogLock.lock();
        try {
          HLogSplitter splitter = HLogSplitter.createLogSplitter(
            conf, rootdir, logDir, oldLogDir, this.fs);
          try {
            // If FS is in safe mode, just wait till out of it.
            FSUtils.waitOnSafeMode(conf, conf.getInt(HConstants.THREAD_WAKE_FREQUENCY, 1000));
            splitter.splitLog();
          } catch (OrphanHLogAfterSplitException e) {
            LOG.warn("Retrying splitting because of:", e);
            //An HLogSplitter instance can only be used once.  Get new instance.
            splitter = HLogSplitter.createLogSplitter(conf, rootdir, logDir,
              oldLogDir, this.fs);
            splitter.splitLog();
          }
          splitTime = splitter.getTime();
          splitLogSize = splitter.getSize();
        } finally {
          this.splitLogLock.unlock();
        }
      }
    }

    if (this.metrics != null) {
      this.metrics.addSplit(splitTime, splitLogSize);
    }
  }