HDFS-13175. Add more information for checking argument in DiskBalancerVolume.

Contributed by  Lei (Eddy) Xu.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/diskbalancer/command/PlanCommand.java

@@ -124,6 +124,14 @@ public class PlanCommand extends Command {
       throw new IllegalArgumentException("Unable to find the specified node. " +
           cmd.getOptionValue(DiskBalancerCLI.PLAN));
     }
+
+    try (FSDataOutputStream beforeStream = create(String.format(
+        DiskBalancerCLI.BEFORE_TEMPLATE,
+        cmd.getOptionValue(DiskBalancerCLI.PLAN)))) {
+      beforeStream.write(getCluster().toJson()
+          .getBytes(StandardCharsets.UTF_8));
+    }
+
     this.thresholdPercentage = getThresholdPercentage(cmd);
 
     LOG.debug("threshold Percentage is {}", this.thresholdPercentage);
@@ -138,14 +146,6 @@ public class PlanCommand extends Command {
       plan = plans.get(0);
     }
 
-
-    try (FSDataOutputStream beforeStream = create(String.format(
-        DiskBalancerCLI.BEFORE_TEMPLATE,
-        cmd.getOptionValue(DiskBalancerCLI.PLAN)))) {
-      beforeStream.write(getCluster().toJson()
-          .getBytes(StandardCharsets.UTF_8));
-    }
-
     try {
       if (plan != null && plan.getVolumeSetPlans().size() > 0) {
         outputLine = String.format("Writing plan to:");

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/diskbalancer/connectors/DBNameNodeConnector.java

@@ -144,8 +144,6 @@ class DBNameNodeConnector implements ClusterConnector {
       // Does it make sense ? Balancer does do that. Right now
       // we only deal with volumes and not blockPools
 
-      volume.setUsed(report.getDfsUsed());
-
       volume.setUuid(storage.getStorageID());
 
       // we will skip this volume for disk balancer if

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/diskbalancer/datamodel/DiskBalancerVolume.java

@@ -269,7 +269,9 @@ public class DiskBalancerVolume {
    * @param dfsUsedSpace - dfsUsedSpace for this volume.
    */
   public void setUsed(long dfsUsedSpace) {
-    Preconditions.checkArgument(dfsUsedSpace < this.getCapacity());
+    Preconditions.checkArgument(dfsUsedSpace < this.getCapacity(),
+        "DiskBalancerVolume.setUsed: dfsUsedSpace(%s) < capacity(%s)",
+        dfsUsedSpace, getCapacity());
     this.used = dfsUsedSpace;
   }