Namenode

Namenode

Name node,

• What it stores
• What it not stores
• What is the responsible
• How many name nodes
• Production environment
• If heart fails then what the result
• Why Name node is high-expensive 

Stores

• Name node is a master daemon, it is the heart of HDFS file system.
• Name node stores the all files information’s which presents in HDFS. 
• This file information we can say metadata as well, means Namenode stores the metadata about the files. 
• Namenode is the point of contact for any hadoop files

Not stores

• Namenode not stores raw data or actual data. 

Responsible 

• We know file blocks are stored in Data Nodes, these data nodes maintains and manage by NameNode.
• Client application communicates to name node to do file operations like add, copy, move, delete file.
• Name node used to provide the required metadata to client.

How many

• Only one name node per cluster.

Production

• In production environment name node runs on separate machine.

If Namenode fails

• As per the discussion Namenode is the heart of the HDFS, so if heart fails then we know well about the next condition.
• Name node is a single point of failure, means if name node fails then accessing file system is not at all possible. 

Why Namenode is high expensive

• Namenode should run in high end machine.
• Reason why Namenode high expensive
• Name node is a Single Point of Failure. (SPOF) 
• Namenode holds metadata for quick response, so more memory is required.
• Name node organizes hundreds or thousands of data nodes and respond to client requests.
• Name node have to maintain load balance, by considering all reasons, name node required high expensive machine.
• Based on requirement we can scaled-up machine for a name node.

Thanks for your time. 

Nireekshan