What messages are transacted between NameNode and DataNode?

DataNodes sends information to the NameNode about the files and blocks stored in that node and responds to the NameNode for all filesystem operations. 6. When a DataNode starts up it announce itself to the NameNode along with the list of blocks it is responsible for.

How does DataNode communicate with NameNode?

All communication between Namenode and Datanode is initiated by the Datanode, and responded to by the Namenode. The Namenode never initiates communication to the Datanode, although Namenode responses may include commands to the Datanode that cause it to send further communications.

What information heartbeat carries from DataNode to NameNode?

NameNode that receives the Heartbeats from a DataNode also carries information like total storage capacity, the fraction of storage in use, and the number of data transfers currently in progress. For the NameNode’s block allocation and load balancing decisions, we use these statistics.

What is role of 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.

What is DataNode and NameNode?

The main difference between NameNode and DataNode in Hadoop is that the NameNode is the master node in Hadoop Distributed File System (HDFS) that manages the file system metadata while the DataNode is a slave node in Hadoop distributed file system that stores the actual data as instructed by the NameNode.

What are the responsibilities of NameNode and DataNode secondary name node in Hadoop Distributed File System?

DataNode is responsible for storing the actual data in HDFS. NameNode and DataNode are in constant communication. When a DataNode is down, it does not affect the availability of data or the cluster. NameNode will arrange for replication for the blocks managed by the DataNode that is not available.

What information is included in a heartbeat from Task Tracker to job tracker?

The TaskTrackers send out heartbeat messages to the JobTracker, usually every few minutes, to reassure the JobTracker that it is still alive. These message also inform the JobTracker of the number of available slots, so the JobTracker can stay up to date with where in the cluster work can be delegated.

What is NameNode in Hadoop architecture?

NameNode is the master node in the Apache Hadoop HDFS Architecture that maintains and manages the blocks present on the DataNodes (slave nodes). NameNode is a very highly available server that manages the File System Namespace and controls access to files by clients.

What does the NameNode do in Hadoop?

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.

What is HDFS DataNode?

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.