HDFS Server

In the context of Hadoop and Hadoop Distributed File System (HDFS), there are specific roles or components that collectively make up the HDFS cluster. One of these roles is the “HDFS Server.” Here’s an overview of what an HDFS server refers to:

1. HDFS Architecture: HDFS is designed as a distributed file system that spans across multiple servers in a Hadoop cluster. The architecture typically consists of two main types of servers: NameNode and DataNode.

2. NameNode: The NameNode is often referred to as the “HDFS server” because it plays a central and critical role in the HDFS architecture. There is typically only one active NameNode in an HDFS cluster (with a secondary NameNode for fault tolerance). The primary responsibilities of the NameNode are:

   • Maintaining the metadata of the file system, including the directory structure, file permissions, and ownership.
   • Keeping track of the structure of the HDFS filesystem and the location of data blocks.
   • Coordinating client read and write requests and providing data block locations to DataNodes.

3. DataNode: DataNodes are the worker nodes in the HDFS cluster and are responsible for storing and serving the actual data blocks. Each server that runs a DataNode service is essentially an HDFS server as well. DataNodes:

   • Store and manage the data blocks that make up files in HDFS.
   • Periodically report to the NameNode about the status of the data blocks they manage, including block replication and availability.

4. Secondary NameNode: While not a primary HDFS server, the Secondary NameNode is another server that helps maintain the integrity of the HDFS filesystem by periodically merging the edits log with the fsimage to create a new checkpoint. This operation helps in reducing recovery time in case of a NameNode failure.