When a NameNode fails to receive a pulse from a DataNode?

When NameNode notices that it has not received a heartbeat message from a data node after a certain amount of time, the data node is marked as dead. Since blocks will be under-replicated the system begins replicating the blocks that were stored on the dead DataNode.

How does NameNode tackle DataNode failures and what will you do when NameNode is down?

Basic Operations of Datanode:

1. Datanodes is responsible of storing actual data.
2. Upon instruction from Namenode, it performs operations like creation/replication/deletion of data blocks.
3. When one of Datanode gets down then it will not make any effect on Hadoop cluster due to replication.

What happens if a DataNode fails?

If a DataNode fails to heartbeat for reasons other than disk failure, it needs to be recommissioned to be added back to the cluster. If a DataNode rejoins the cluster, there is a possibility for surplus replicas of blocks that were on that DataNode.

How do you deal with NameNode failure?

But since Hadoop 2, you have a better way to handle failures in the NameNode . 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 .

How do you recover a name node 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.

What happens when the NameNode on the Hadoop cluster goes down?

When the NameNode goes down, the file system goes offline. There is an optional SecondaryNameNode that can be hosted on a separate machine. It only creates checkpoints of the namespace by merging the edits file into the fsimage file and does not provide any real redundancy.

What would happen if NameNode failed How do you bring it up?

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.

Can you access cluster and data if NameNode is down?

There are daemons in Hadoop, Namenode, data node, Resource manager, AppMaster and etc. So if Namenode is down (Master node), then the data remains as is in the cluster, BUT you will not be able to access it at all.

What happens if name node goes down?

Can you recover a NameNode when it is down?

When a name node fails, it is possible to recover from a previous checkpoint generated by Secondary Namenode. Secondary Namenode performs periodic checkpoint process.

What would happen if NameNode crashes in a HDFS cluster?

Since there is only one NameNode, it is the single point of failure in a HDFS cluster. When NameNode crashes, system may become unavailable. We can specify a secondary NameNode in HDFS cluster.

What will happen with a NameNode that doesn’t have any data?

What happens to a NameNode that has no data? Answer:There does not exist any NameNode without data. If it is a NameNode then it should have some sort of data in it.

How does NameNode tackle DataNode failures in Hadoop?

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.

When does NameNode assume a data node is dead?

Data node passes a heartbeat signal to Name node in an interval of 2 minutes.When Name node does not receive heartbeat signals from Data node, it assumes that the data node is either dead or non-functional.

How does a block report work in NameNode?

A block report contains a list of all blocks on a datanode. Data node passes a heartbeat signal to Name node in an interval of 2 minutes.When Name node does not receive heartbeat signals from Data node, it assumes that the data node is either dead or non-functional.

How does DataNode work in a HDFS cluster?

The client writes data to one slave node and then it is responsibility of Datanode to replicates data to the slave nodes according to replication factor. An HDFS cluster has two types of nodes operating in a master−slave pattern: