What is swapping in Hadoop?

This new feature gives Hadoop admins the commonplace ability to replace failed DataNode drives without unscheduled downtime. Hot swapping—the process of replacing system components without shutting down the system—is a common and important operation in modern, production-ready systems.

Why do the nodes are removed and added frequently in a Hadoop cluster?

Basically, in a Hadoop cluster a Manager node will be deployed on a reliable hardware with high configurations, the Slave node’s will be deployed on commodity hardware. So chance’s of data node crashing is more . So more frequently you will see admin’s remove and add new data node’s in a cluster.

How do you decommission a node in Hadoop?

Decommissioning process of the data node ensures that data is transferred to other nodes so that the existing replication factor is not disturbed.

1. Check NameNode UI for available data nodes and their status.
2. dfs.hosts.exclude property.
3. Update dfs.exclude file.
4. Run refreshNodes command.

How does Hadoop increase cluster size?

The most common practice to size a Hadoop cluster is sizing the cluster based on the amount of storage required. The more data into the system, the more will be the machines required. Each time you add a new node to the cluster, you get more computing resources in addition to the new storage capacity.

What is reduce phase in Map-Reduce?

Map-Reduce is a programming model that is mainly divided into two phases i.e. Map Phase and Reduce Phase. It is designed for processing the data in parallel which is divided on various machines(nodes). The Hadoop Java programs are consist of Mapper class and Reducer class along with the driver class.

How do I stop Nodejs data?

1 Answer

1. start-all.sh & stop-all.sh. Used to start and stop Hadoop daemons all at once.
2. start-dfs.sh, stop-dfs.sh and start-yarn.sh, stop-yarn.sh.
3. hadoop-daemon.sh namenode/datanode and yarn-deamon.sh resourcemanager.
4. Note : You should have ssh enabled if you want to start all the daemons on all the nodes from one machine.

How is HDFS tolerant?

HDFS is highly fault-tolerant. It creates a replica of users’ data on different machines in the HDFS cluster. So whenever if any machine in the cluster goes down, then data is accessible from other machines in which the same copy of data was created.

How add and remove nodes in Hadoop?

3 Answers

1. Shut down the NameNode.
2. Set dfs.
3. Restart NameNode.
4. In the dfs exclude file, specify the nodes using the full hostname or IP or IP:port format.
5. Do the same in mapred.exclude.
6. execute bin/hadoop dfsadmin -refreshNodes .
7. execute bin/hadoop mradmin -refreshNodes.