Reason of Formatting Namenode

[Adarsh Sharma]

Dear all,

I have configured several times a Hadoop Cluster of 2,3,5,8 nodes but 
one doubt in my mind always occur.
Why it is necessary to format Hadoop Namenode by *bin/hadoop -namenode 
format *command.
What is the reason and logic behind this.
Please justify if someone knows.


Thanks & best Regards,

Adarsh Sharma