How to set Maintenance
      Mode for a service and what happens when you do.
      Setting Maintenance Mode enables you to suppress alerts and
         omit bulk operations for specific services, components, and hosts in an Ambari-managed
         cluster. Explicitly setting Maintenance Mode for a service implicitly sets Maintenance Mode
         for components and hosts that run the service. While Maintenance Mode prevents bulk
         operations being performed on the service, component, or host, you may explicitly start and
         stop a service, component, or host while in Maintenance Mode.- 
            Using Services, click a service name.
            For example, HDFS. 
- 
            Click Actions, then click Turn On Maintenance
                  Mode.
         
- 
            Click OK to confirm.
            Notice, on Services Summary that Maintenance Mode turns on
               for the NameNode and SNameNode components.