Block – Block is the continuous location on the hard drive where data HDFS store data. In general, FileSystem store data as a collection of blocks. In a similar way, HDFS stores each file as blocks, and distributes it across the Hadoop cluster.
InputSplit- InputSplit represents the data which individual Mapper will process. Further split divides into records. Each record (which is a key-value pair) will be processed by the map.
Block- It is the physical representation of data.
InputSplit- It is the logical representation of data. Thus, during data processing in MapReduce program or other processing techniques use InputSplit. In MapReduce, important thing is that InputSplit does not contain the input data. Hence, it is just a reference to the data.
Block- The default size of the HDFS block is 128 MB which is configured as per our requirement. All blocks of the file are of the same size except the last block. The last Block can be of same size or smaller. In Hadoop, the files split into 128 MB blocks and then stored into Hadoop Filesystem.
InputSplit- Split size is approximately equal to block size, by default.
Hope it helps