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 only to the
following service roles, other roles running on the host are stopped:
HDFS DataNode
MapReduce TaskTracker
YARN NodeManager
HBase RegionServer
Kafka Broker
Decommissioning only applies to the Kafka Broker role if Cruise Control
is installed on the cluster. When a Kafka Broker role is decommissioned, Cruise
Control moves the data and partitions from the selected broker role to other broker
roles in the cluster. For more information about decommissioning Kafka brokers, see
Scaling Kafka brokers.
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.
Minimum Required Role:Limited
Operator (also provided by
Operator, Configurator,
Cluster Administrator, Limited
Cluster Administrator , or Full
Administrator).
To decommission one or more hosts:
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.
In Cloudera Manager, select the cluster where you want to
decommission hosts.
In the left menu, click Hosts > All
Hosts.
Select the hosts that you want to decommission.
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.
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.
Click Begin Maintenance.
The Host Decommission Command
dialog box opens and displays the progress of the
command.