HDFS-13153. Enable HDFS diskbalancer by default. Contributed by Ajay Kumar.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -1146,7 +1146,7 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   // Disk Balancer Keys
   public static final String DFS_DISK_BALANCER_ENABLED =
       "dfs.disk.balancer.enabled";
-  public static final boolean DFS_DISK_BALANCER_ENABLED_DEFAULT = false;
+  public static final boolean DFS_DISK_BALANCER_ENABLED_DEFAULT = true;
 
   public static final String DFS_DISK_BALANCER_MAX_DISK_THROUGHPUT =
       "dfs.disk.balancer.max.disk.throughputInMBperSec";

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

@@ -4633,10 +4633,10 @@
 
   <property>
     <name>dfs.disk.balancer.enabled</name>
-    <value>false</value>
+    <value>true</value>
     <description>
         This enables the diskbalancer feature on a cluster. By default, disk
-      balancer is disabled.
+      balancer is enabled.
     </description>
   </property>