Hey,
For me, my Hadoop NameNode was in safe mode. That is a read-only mode for the HDFS cluster. It can't Write, until enough datanode up for replication After started up enough datanode still my NameNode in safe mode, just manually OFF safe mode by
root@localhost:/opt/hadoop-2.2.0# bin/hadoop dfsadmin -safemode leave
Just check the inconsistency of HDFS cluster by
[bin]#root@localhost:/opt/hadoop-2.2.0# bin/hadoop fsck /