HDFS-7875. Improve log message when wrong value configured for dfs.datanode.failed.volumes.tolerated. Contributed by Nijel.

(cherry picked from commit 2da3d2ed2ff2e9b48dbda7e029aa58261c729d35)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -8,6 +8,10 @@ Release 2.8.0 - UNRELEASED
 
   IMPROVEMENTS
 
+    HDFS-7875. Improve log message when wrong value configured for
+    dfs.datanode.failed.volumes.tolerated.
+    (nijel via harsh)
+
     HDFS-2360. Ugly stacktrace when quota exceeds. (harsh)
 
     HDFS-7835. make initial sleeptime in locateFollowingBlock configurable for

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java

@@ -278,8 +278,10 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
     this.validVolsRequired = volsConfigured - volFailuresTolerated;
 
     if (volFailuresTolerated < 0 || volFailuresTolerated >= volsConfigured) {
-      throw new DiskErrorException("Invalid volume failure "
-          + " config value: " + volFailuresTolerated);
+      throw new DiskErrorException("Invalid value configured for "
+          + "dfs.datanode.failed.volumes.tolerated - " + volFailuresTolerated
+          + ". Value configured is either less than 0 or >= "
+          + "to the number of configured volumes (" + volsConfigured + ").");
     }
     if (volsFailed > volFailuresTolerated) {
       throw new DiskErrorException("Too many failed volumes - "