DataNode
A DataNode is a fundamental component of the Hadoop Distributed File System (HDFS) architecture. Within the Master-Slave Architecture employed by Apache Hadoop, the DataNode serves as the worker node responsible for storing and managing the actual data blocks on local disk drives. Unlike the NameNode, which manages metadata, the DataNode handles the heavy lifting of data storage and retrieval.
The primary responsibilities of a DataNode include responding to read and write requests from clients and performing block-level operations such as creation, deletion, and replication as directed by the NameNode. According to the official Apache HDFS architecture documentation, these nodes communicate their status through periodic heartbeats. If a DataNode fails to send a heartbeat, the system assumes the node is down and begins the process of Block Replication on other healthy nodes to maintain Fault Tolerance.
In a large-scale Big Data environment, a cluster may contain thousands of DataNodes. These nodes are often organized into racks to optimize network bandwidth and ensure data reliability through rack-aware replication policies. This distributed approach allows for massive scalability and high throughput for Parallel Processing tasks, such as those performed by MapReduce or Apache Spark. Further technical details regarding node management can be found via IBM's overview of HDFS.