Quick Answer: What Is NameNode And DataNode?

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 happens if secondary NameNode fails?

If NameNode is failed, File System metadata can be recovered from the last saved FsImage on the Secondary NameNode but Secondary NameNode can’t take the primary NameNode’s functionality.

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.

What is HDFS and how it works?

The way HDFS works is by having a main « NameNode » and multiple « data nodes » on a commodity hardware cluster. … Data is then broken down into separate « blocks » that are distributed among the various data nodes for storage. Blocks are also replicated across nodes to reduce the likelihood of failure.

Which NameNode is used when the primary NameNode goes down?

________ NameNode is used when the Primary NameNode goes down. Explanation: Secondary namenode is used for all time availability and reliability.

What is a DataNode in Hadoop?

DataNodes store data in a Hadoop cluster and is the name of the daemon that manages the data. File data is replicated on multiple DataNodes for reliability and so that localized computation can be executed near the data. Within a cluster, DataNodes should be uniform.

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

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. NameNode periodically receives a Heartbeat and a Data Blocks report from each of the DataNodes in the cluster in an interval of specified time.

What is InputSplit in Hadoop?

InputSplit in Hadoop MapReduce is the logical representation of data. It describes a unit of work that contains a single map task in a MapReduce program. Hadoop InputSplit represents the data which is processed by an individual Mapper. The split is divided into records.

What kind of information is stored in NameNode?

NameNode is the centerpiece of HDFS. NameNode only stores the metadata of HDFS – the directory tree of all files in the file system, and tracks the files across the cluster. NameNode does not store the actual data or the dataset. The data itself is actually stored in the DataNodes.

What are the features of HDFS?

The key features of HDFS are:Cost-effective: … Large Datasets/ Variety and volume of data. … Replication. … Fault Tolerance and reliability. … High Availability. … Scalability. … Data Integrity. … High Throughput.More items…

What are the goals of HDFS?

The goals of HDFSFast recovery from hardware failures. Because one HDFS instance may consist of thousands of servers, failure of at least one server is inevitable. … Access to streaming data. … Accommodation of large data sets. … Portability.

What is 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. It does not store the data of these files itself. … The NameNode is a Single Point of Failure for the HDFS Cluster.

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.

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 <-> DataNodeDataNode sends heartbeat. The DataNode sends a heartbeat message every few seconds. … DataNode sends block report. … DataNode notifies BlockReceived.

Why is Hdfs needed?

As we know HDFS is a file storage and distribution system used to store files in Hadoop environment. It is suitable for the distributed storage and processing. Hadoop provides a command interface to interact with HDFS. The built-in servers of NameNode and DataNode help users to easily check the status of the cluster.