11. What is the difference between HDFS block and InputSplit?
An HDFS block splits data into physical divisions while InputSplit in MapReduce splits input files logically.
While InputSplit is used to control number of mappers, the size of splits is user defined. On the contrary, the HDFS block size is fixed to 64 MB, i.e. for 1GB data , it will be 1GB/64MB = 16 splits/blocks. However, if input split size is not defined by user, it takes the HDFS default block size.
