code: void registerMBean(final String storageId) {
      // We wrap to bypass standard mbean naming convetion.
      // This wraping can be removed in java 6 as it is more flexible in
      // package naming for mbeans and their impl.
      StandardMBean bean;
      String storageName;
      if (storageId == null || storageId.equals("")) {// Temp fix for the uninitialized storage
        storageName = "UndefinedStorageId" + rand.nextInt();
      } else {
        storageName = storageId;
      }
      try {
        bean = new StandardMBean(this,FSDatasetMBean.class);
        mbeanName = MBeanUtil.registerMBean("DataNode", "FSDatasetState-" + storageName, bean);
        versionBeanName = VersionInfo.registerJMX("DataNode");
      } catch (NotCompliantMBeanException e) {
        e.printStackTrace();
      }
  
      DataNode.LOG.info("Registered FSDatasetStatusMBean");
    }
docs: Register the FSDataset MBean using the name
  "hadoop:service=DataNode,name=FSDatasetState-<storageid>"