HDFS File Block and Input Split

Blocks are physical division and input splits are logical division. One input split can be map to multiple physical blocks. When Hadoop submits jobs, it splits the input data logically and process by each Mapper task. The number of Mappers are equal to the number of splits. One important thing to remember is that InputSplit doesn’t contain actual data but a reference (storage locations) to the data. A split basically has 2 things :