HDFS-3677. dfs.namenode.edits.dir.required is missing from hdfs-default.xml. Contributed by Mark Yang.

(cherry picked from commit 414f33126ac178a44146666cc7c00059cfc9cabf)
(cherry picked from commit 41621a994dd3add51ec95a3136070c148b133726)

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -383,6 +383,15 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.namenode.edits.dir.required</name>
+  <value></value>
+  <description>This should be a subset of dfs.namenode.edits.dir,
+      to ensure that the transaction (edits) file
+      in these places is always up-to-date.
+  </description>
+</property>
+
 <property>
   <name>dfs.namenode.shared.edits.dir</name>
   <value></value>