Does it create a new block?
The smallest amount of data that MapR will write is a block, which is 8 KB. If you store a file that is not evenly divisible by 8KB, the last block of a write will contain some empty space. When you append data, that write will start with a new block.
When we try to append data to an already existing block then namenode check the file’s last block. If the last block is not full and has replicas then namenode changes this block to be an under construction block along with its replicas as its initial pipeline and starts writing the data to it.
If the last block is full then namenode creates a new block and writes data.
Retrieving data ...