HDFS-10633. DiskBalancer : Add the description for the new setting dfs.disk.balancer.plan.threshold.percent in HDFSDiskbalancer.md. Contributed by Yiqun Lin.

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

@@ -4294,8 +4294,10 @@
     <name>dfs.disk.balancer.plan.threshold.percent</name>
     <value>10</value>
     <description>
-        The percentage that disk tolerance that we are ok with in
-      a plan.
+      The percentage threshold value for volume Data Density in a plan.
+      If the absolute value of volume Data Density which is out of
+      threshold value in a node, it means that the volumes corresponding to
+      the disks should do the balancing in the plan. The default value is 10.
     </description>
   </property>
 

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSDiskbalancer.md

@@ -125,6 +125,7 @@ There is a set of diskbalancer settings that can be controlled via hdfs-site.xml
 |`dfs.disk.balancer.max.disk.throughputInMBperSec` | This controls the maximum disk bandwidth consumed by diskbalancer while copying data. If a value like 10MB is specified then diskbalancer on the average will only copy 10MB/S. The default value is 10MB/S.|
 |`dfs.disk.balancer.max.disk.errors`| sets the value of maximum number of errors we can ignore for a specific move between two disks before it is abandoned. For example, if a plan has 3 pair of disks to copy between , and the first disk set encounters more than 5 errors, then we abandon the first copy and start the second copy in the plan. The default value of max errors is set to 5.|
 |`dfs.disk.balancer.block.tolerance.percent`| The tolerance percent specifies when we have reached a good enough value for any copy step. For example, if you specify 10% then getting close to 10% of the target value is good enough.|
+|`dfs.disk.balancer.plan.threshold.percent`| The percentage threshold value for volume Data Density in a plan. If the absolute value of volume Data Density which is out of threshold value in a node, it means that the volumes corresponding to the disks should do the balancing in the plan. The default value is 10.|
 
  Debugging
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