A block is nothing but the smallest continuous file location where data resides. A file is split up into blocks (default 64MB or 128 MB) and stored as independent units in a distributed fashion across multiple systems. These blocks replicate as per the replication factor. After replication, it is stored at different nodes. This handles the failure in the cluster. Let us say we have a file of size 612 MB, and we are using the default block configuration (128 MB). Therefore, five blocks are created, the first four blocks are 128 MB in size, and the fifth block is 100 MB in size (128*4+100=612). From the above example, we can conclude that: A file in HDFS, smaller than a single block does not occupy a full block size space of the underlying storage. Each file stored in HDFS does not need to be an exact multiple of the configured block size.  Hadoop 1 default block size: 64MB  Hadoop 2 default block size: 128 MB  Yes, we can configure the block size as per our requirement by changing the dfs.block.size property in hdfs.xml in a hadoop ecosystem.   The following are the advantages of hadoop data blocks:  No limitation on the file size.  Simplicity of storage subsystem.  Eliminating metadata concerns.