How file gets stored in HDFS

• Image a big text file
• File is broken up into several blocks of data(Chunks).
• each block is stored in different node in a cluster
• Advantage of doing this 
  • Each block is of equal size. Allows HDFS to deal with bigger files in the same way. 
  • Makes storage in simple. 
  • Only keep multiple copy of block not the whole file in different node. 
  • Always dealing with same about of data - Good for processes and equal processing time
• Optimum block size is 128 MB
• Namenode contains mapping of blocks in datanode