According to the HBase book () :
HBase will lose data unless it is running on an HDFS that has a durable sync implementation. Hadoop 0.20.2, Hadoop 0.20.203.0, and Hadoop 0.20.204.0 DO NOT have this attribute. Currently only Hadoop versions 0.20.205.x or any release in excess of this version – this includes hadoop 1.0.0 – have a working, durable sync . Sync has to be explicitly enabled by setting dfs.support.append equal to true on both the client side – in hbase-site.xml – and on the serverside in hdfs-site.xml (The sync facility HBase needs is a subset of the append code path).