Aug 9, 2016
HDFS hflush vs hsync
hflush: This API flushes all outstanding data (i.e. the current unfinished packet) from the client into the OS buffers on all DataNode replicas.
hsync: This API flushes the data to the DataNodes, like hflush(), but should also force the data to underlying physical storage via fsync (or equivalent). Note that only the current block is flushed to the disk device.
[1] https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSOutputStream.java