Minimum Required Role: Limited Operator (also provided by Operator, Configurator, Cluster Administrator, or Full Administrator)

Note that the Limited Operator and Operator roles do not allow you to suppress or enable alerts.

  Note: Hosts with DataNodes and DataNode roles themselves can only be decommissioned if the resulting action leaves enough DataNodes commissioned to maintain the configured HDFS replication factor (by default 3). If you attempt to decommission a DataNode or a host with a DataNode in such situations, the decommission process will not complete and must be aborted.

Cloudera Manager manages the host decommission and recommission process and allows you the option to specify whether to replicate the data to other DataNodes, and whether or not to suppress alerts.

Decommissioning a host decommissions and stops all roles on the host without requiring you to individually decommission the roles on each service. Decommissioning applies to only to HDFS DataNode, MapReduce TaskTracker, YARN NodeManager, and HBase RegionServer roles. If the host has other roles running on it, those roles are stopped.

To decommission one or more hosts:

1. If the host has a DataNode, and you are planning to replicate data to other hosts (for longer term maintenance operations or to permanently decommission or repurpose the host), perform the steps in Tuning HDFS Prior to Decommissioning DataNodes.
2. In Cloudera Manager, select the cluster where you want to decommission hosts.
3. Click Hosts > All Hosts.
4. Select the hosts that you want to decommission.
5. Select Actions for Selected > Begin Maintenance (Suppress Alerts/Decommission.

   (If you are logged in as a user with the Limited Operator or Operator role, the menu item is labeled Decommission Host(s) and you will not see the option to suppress alerts.)

   The Begin Maintenance (Suppress Alerts/Decommission) dialog box opens. The role instances running on the hosts display at the top.

6. To decommission the hosts and suppress alerts, select Decommission Host(s). When you select this option for hosts running a DataNode role, choose one of the following (if the host is not running a DataNode role, you will only see the Decommission Host(s) option:):
   • Decommission DataNodes

     This option re-replicates data to other DataNodes in the cluster according to the configured replication factor. Depending on the amount of data and other factors, this can take a significant amount of time and uses a great deal of network bandwidth. This option is appropriate when replacing disks, repurposing hosts for non-HDFS use, or permanently retiring hardware.

   • Take DataNode Offline
     This option does not re-replicate HDFS data to other DataNodes until the amount of time you specify has passed, making it less disruptive to active workloads. After this time has passed, the DataNode is automatically recommissioned, but the DataNode role is not started. This option is appropriate for short-term maintenance tasks such not involving disks, such as rebooting, CPU/RAM upgrades, or switching network cables.

     CAUTION:

     Taking multiple DataNodes offline simultaneously increases the chances that some HDFS data may become unavailable during maintenance. Configuring the proper value for the Maintenance State Minimal Block Replication HDFS configuration property will avoid risking data availability. See Cloudera Manager Configuration Properties.
7. Click Begin Maintenance.

   The Host Decommission Command dialog box opens and displays the progress of the command.

  Note:

• You cannot start roles on a decommissioned host.
• When a DataNode is decommissioned, although HDFS data is replicated to other DataNodes, local files containing the original data blocks are not automatically removed from the storage directories on the host. If you want to permanently remove these files from the host to reclaim disk space, you must do so manually.

Minimum Required Role: Operator (also provided by Configurator, Cluster Administrator, Full Administrator)

Only hosts that are decommissioned using Cloudera Manager can be recommissioned.

1. In Cloudera Manager, select the cluster where you wan to recommission hosts.
2. Click Hosts > All Hosts.
3. Select the hosts that you want to recommission.
4. Select Actions for Selected > End Maintenance (Suppress Alerts/Decommission.

   The End Maintenance (Suppress Alerts/Decommission dialog box opens. The role instances running on the hosts display at the top.

5. To recommission the hosts, select Recommission Host(s).
6. Choose one of the following:
   • Bring hosts online and start all roles

     All decommissioned roles will be recommissioned and started. HDFS DataNodes will be started first and brought online before decommissioning to avoid excess replication.

   • Bring hosts online

     All decommissioned roles will be recommissioned but remain stopped. You can restart the roles later.

7. Click End Maintenance.

   The Recommission Hosts and Start Roles Command dialog box opens and displays the progress of recommissioning the hosts and restarting the roles.

Minimum Required Role: Operator (also provided by Configurator, Cluster Administrator, Full Administrator)

1. Click the Hosts tab.
2. Select one or more hosts on which to stop all roles.
3. Select Actions for Selected > Stop Roles on Hosts.

Minimum Required Role: Operator (also provided by Configurator, Cluster Administrator, Full Administrator)

1. Click the Hosts tab.
2. Select one or more hosts on which to start all roles.
3. Select Actions for Selected > Start Roles on Hosts.