Hadoop Distributed File System (HDFS) is a system that stores big data across many computers. The main part is the NameNode, which keeps track of files and controls who can see them. The other computers, called DataNodes, hold the data and let clients read or write it.

When a client wants to work with a file, it talks to the NameNode to find out where the data is located. Then it goes straight to the DataNodes to get or change the data.

HDFS can store very large files by breaking them into blocks and putting each block on different DataNodes. It keeps copies of the data on multiple DataNodes so that if one fails, the data is still available.

The NameNode keeps important information about the file system, like where the data is and who can see it. It also keeps track of which DataNodes are working properly.

There’s also another part of HDFS called the Secondary NameNode. It makes a copy of the important information in case the NameNode fails.

HDFS is great for handling big data because it can store and share data across many computers, which makes it reliable and fast.