First of all,
Let us begin with the architecture.
Now the above image represents the architecture of Hadoop.
Let me explain u in detail.
Here you have the following
- Name Node
- Data Node
- Secondary Name Node
Secondary Name Node acts as a buffer to the Name Node, Not as its Back up. It stores the intermediate updates of the FS in a file called edit-log and updates them to the Final FS Image when Name Node is inactive.
We are currently updated to Hadoop Version 2.x and it is no more related to the Secondary Name Node. It is replaced by the Standby Name node Which acts as a stand by to the actual name node and handles the Name Node Failures.