To save the HDFS namepsace:
Place the NameNode in safe mode, to keep HDFS from accepting any new writes:
hadoop dfsadmin -safemode enter
Save the namespace.
hadoop dfsadmin -saveNamespace
Note Do NOT leave safe mode from this point onwards. HDFS should not accept any new writes.
On the machine that hosts the NameNode, copy the following checkpoint directories into a backup directory:
<HDP data directory>/hdfs/nn/edits/current <HDP data directory>/hdfs/nn/edits/image <HDP data directory>/hdfs/nn/edits/previous.checkpoint