Hadoop DataNode

In this chapter

Following aspects of DataNode are explained in this chapter

What is DataNode ?

A DataNode stores data in the HDFS. A functional filesystem has more than one DataNode, with data replicated across them. On start-up, a NameNode connects to the DataNodes. It then responds to requests from the NameNode for filesystem operations. Client applications can talk directly to a DataNode, once the NameNode has provided the location of the data.

To manage DataNodes on your cluster, go to HDFS > DataNode.

data-node

DataNode Summary

Following details are displayed in DataNode summary:

Add DataNode

Click on "Add" button to add DataNode to the cluster.

Start/Stop DataNode

To start or stop a DataNode, select the check box against the node and click on Start or Stop button respectively.

Delete DataNode

To delete a DataNode from the cluster, select the check box against the the DataNode and click Delete. But to delete a DataNode, it must be first decommissioned.
Click here to know more about node replacement and deleting a DataNode.

Start/Stop Monitoring

JMX monitoring takes place which checks DataNode's status, CPU Usage, RAM, N/W Rcvd, N/W Sent, Disk Read, Disk Write, Disk Usage, Bytes Read and Bytes Written. To start or stop DataNode Monitoring, select the check box against the node and click on Start Monitoring or Stop Monitoring button respectively.

Decommission

Before a node can be deleted, it must be decommissioned. When a DataNode is decommissioned, HDFS will copy all its data to other DataNodes(if any) and updates the NameNode data. Decommissioned node will no longer be valid for storing data, but will be a part of cluster until it is deleted.
To decommission a node, select the DataNode and click Decommission.

DataNode Details

DataNode in the menu displays all the DataNodes in the HDFS cluster. Just click on the DataNode name in the menu to get all the details of the DataNode system. Details are displayed in form of charts.

DataNode details contain:

DataNode-charts

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