Write
Operation:-
* Client node interacts with namenode
* Namenode provides address of the data nodes on which the write operation
should take place
* Once client receives the data nodes address, it starts to write the
information directly on data node
* Client node does not write information on the replicas of a Block ,
it writes only to one block
* The datanodes or
slaves know how to share or copy the data from each other. Basically, the slave
nodes start to replicate among themselves
At API level, The client sends a request to the distributed file
system to fetch address related details about the blocks on slaves.The write
operation uses FSdata
Outputstream to write information to a block. As soon as
the block is written to the first data node/slave, the replica begins to
maintain data consistency among all the blocks in different data nodes
Once the replication process is complete, the acknowledgment is sent from the
last node to the previous node and likewise, it reaches the first node which
sends the final acknowledgment to FS data output-stream.
In case of the crash of a particular datanode , namenode is intelligent enough
to send the address of a active datanode hosting that block for write operation
to smoothly proceed.All along , the namenode is in constant communication with
each of the datanodes or slaves.
