What happens if the NameNode fails?

Whenever the active NameNode fails, the passive NameNode or the standby NameNode replaces the active NameNode, to ensure that the Hadoop cluster is never without a NameNode. The passive NameNode takes over the responsibility of the failed NameNode and keep the HDFS up and running.

What happens when NameNode has no data?

If Namenode gets down then the whole Hadoop cluster is inaccessible and considered dead. Datanode stores actual data and works as instructed by Namenode. A Hadoop file system can have multiple data nodes but only one active Namenode.

How do you fix NameNode when it is down?

Recover Hadoop NameNode Failure

1. Start the namenode in a different host with a empty dfs. name.
2. Point the dfs. name.
3. Use –importCheckpoint option while starting namenode after pointing fs. checkpoint.
4. Change the fs.default.name to the backup host name URI and restart the cluster with all the slave IP’s in slaves file.

How the NameNode failure is handled in the HDFS?

As soon as the data node is declared dead/non-functional all the data blocks it hosts are transferred to the other data nodes with which the blocks are replicated initially. This is how Namenode handles datanode failures. HDFS works in Master/Slave mode where NameNode act as a Master and DataNodes act as a Slave.

Is NameNode a single point of failure?

The single point of failure in a Hadoop cluster is the NameNode. While the loss of any other machine (intermittently or permanently) does not result in data loss, NameNode loss results in cluster unavailability. The permanent loss of NameNode data would render the cluster’s HDFS inoperable.

When NameNode fails which node takes the responsibility of active node?

When active node fails, then Passive node takes the responsibility of active node. Passive node is also called standby namenode that takes the responsibility to remove the problem of single point of failure (SPOF).

What if NameNode fails in Hadoop?

If NameNode gets fail the whole Hadoop cluster will not work. Actually, there will not any data loss only the cluster work will be shut down, because NameNode is only the point of contact to all DataNodes and if the NameNode fails all communication will stop.

What will happen if any data node fails what will happen if the name node fails in Hadoop 1 and Hadoop 2?

What are the problem with NameNode?

Issues That Arise When NameNode Fails When in use, the metadata for HDFS like namespace information, block information, etc. needs to be stored in main memory. But for persistence storage, it needs to be stored in disk.

Which of the following feature overcomes the single point of failure issue of NameNode?

Hadoop High Availability feature tackles the namenode failure problem for all the components in the hadoop stack.

What is NameNode function?

The NameNode is the centerpiece of an HDFS file system. It keeps the directory tree of all files in the file system, and tracks where across the cluster the file data is kept. When the NameNode goes down, the file system goes offline.

What happens when the NameNode fails?

Even the SecondaryNameNode doesn’t help in that case since it’s only used for checkpoints, not as a backup for the NameNode. When the NameNode fails, someone like an administrator would have to manually restart the NameNode. But since Hadoop 2, you have a better way to handle failures in the NameNode.

What is a NameNode in HDFS?

In the article Smattering of HDFS, we learned that NameNode is a single point of failure for the HDFS cluster. Each cluster has a single NameNode and if that machine became unavailable, the whole cluster would become unavailable until the NameNode was restarted or was brought up on a different machine.

Can I run two namenodes alongside one another?

You can run 2 redundant NameNodes alongside one another, so that if one of the Namenodes fails, the cluster will quickly failover to the other NameNode. The way it works is pretty transparent, basically the DataNodes will send reports to both NameNodes so that if one fails, the other one will be ready to be used in active mode.

What is a standby NameNode and how does it work?

The Standby NameNode keeps reading the editLogs from the journal nodes and keeps itself updated. This configuration makes Standby ready to take up the active NameNode role in case of failure. All the DataNodes are configured to send the block report to both of the NameNodes.