What is the Difference Between NameNode and DataNode in Hadoop

The main difference between NameNode and DataNode in Hadoop is that the NameNode is the master node in HDFS that manages the file system metadata while the DataNode is a slave node in HDFS that stores the actual data as instructed by the NameNode. In brief, NameNode controls and manages a single or multiple data nodes.

1. What is DataNode and NameNode in Hadoop?
2. What is the difference between a NameNode and a secondary NameNode?
3. What is a Hadoop NameNode?
4. How a NameNode and DataNode communicate with each other?
5. What is Hadoop interview questions?
6. What is DataNode in Hadoop?
7. What is the use of secondary NameNode?
8. What if NameNode fails in Hadoop?
9. How does NameNode tackle Datanode failures and what will you do when NameNode is down?
10. Is Hadoop a database?
11. What is Hadoop architecture?
12. How do I access Namenode in Hadoop?

What is DataNode and NameNode in Hadoop?

The NameNode keeps an image of the entire file system namespace and file Blockmap in memory. ... The DataNode stores HDFS data in files in its local file system. The DataNode has no knowledge about HDFS files. It stores each block of HDFS data in a separate file in its local file system.

What is the difference between a NameNode and a secondary NameNode?

Secondary namenode is just a helper for Namenode. It gets the edit logs from the namenode in regular intervals and applies to fsimage. Once it has new fsimage, it copies back to namenode. Namenode will use this fsimage for the next restart, which will reduce the startup time.

What is a Hadoop NameNode?

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. ... The NameNode responds the successful requests by returning a list of relevant DataNode servers where the data lives.

How a NameNode and DataNode communicate with each other?

All communication between Namenode and Datanode is initiated by the Datanode, and responded to by the Namenode.
...
4.4 NameNode <-> DataNode

1. DataNode sends heartbeat. The DataNode sends a heartbeat message every few seconds. ...
2. DataNode sends block report. ...
3. DataNode notifies BlockReceived.

What is Hadoop interview questions?

Hadoop Interview Questions

• What are the different vendor-specific distributions of Hadoop? ...
• What are the different Hadoop configuration files? ...
• What are the three modes in which Hadoop can run? ...
• What are the differences between regular FileSystem and HDFS? ...
• Why is HDFS fault-tolerant? ...
• Explain the architecture of HDFS.

What is DataNode in Hadoop?

DataNode: DataNodes are the slave nodes in HDFS. Unlike NameNode, DataNode is a commodity hardware, that is, a non-expensive system which is not of high quality or high-availability. The DataNode is a block server that stores the data in the local file ext3 or ext4.

What is the use of secondary NameNode?

The secondary NameNode merges the fsimage and the edits log files periodically and keeps edits log size within a limit. It is usually run on a different machine than the primary NameNode since its memory requirements are on the same order as the primary NameNode.

What if NameNode fails in Hadoop?

The single point of failure in Hadoop v1 is NameNode. 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.

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

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 Hadoop a database?

Hadoop is not a type of database, but rather a software ecosystem that allows for massively parallel computing. It is an enabler of certain types NoSQL distributed databases (such as HBase), which can allow for data to be spread across thousands of servers with little reduction in performance.

What is Hadoop architecture?

The Hadoop architecture is a package of the file system, MapReduce engine and the HDFS (Hadoop Distributed File System). The MapReduce engine can be MapReduce/MR1 or YARN/MR2. A Hadoop cluster consists of a single master and multiple slave nodes.

How do I access Namenode in Hadoop?

The default address of namenode web UI is http://localhost:50070/. You can open this address in your browser and check the namenode information. The default address of namenode server is hdfs://localhost:8020/. You can connect to it to access HDFS by HDFS api.