diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index b82704cfe51..f95ecd50a94 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -367,6 +367,9 @@ Release 2.0.0 - UNRELEASED
 
     HDFS-3249. Use ToolRunner.confirmPrompt in NameNode (todd)
 
+    HDFS-3179.  Improve the exception message thrown by DataStreamer when 
+    it failed to add a datanode.  (szetszwo)
+
   OPTIMIZATIONS
 
     HDFS-3024. Improve performance of stringification in addStoredBlock (todd)
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSOutputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSOutputStream.java
index 9322143a9ec..40de4cf202d 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSOutputStream.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSOutputStream.java
@@ -128,7 +128,7 @@ class DFSOutputStream extends FSOutputSummer implements Syncable {
   private volatile boolean appendChunk = false;   // appending to existing partial block
   private long initialFileSize = 0; // at time of file open
   private Progressable progress;
-  private short blockReplication; // replication factor of file
+  private final short blockReplication; // replication factor of file
   
   private class Packet {
     long    seqno;               // sequencenumber of buffer in block
@@ -775,9 +775,13 @@ class DFSOutputStream extends FSOutputSummer implements Syncable {
     private int findNewDatanode(final DatanodeInfo[] original
         ) throws IOException {
       if (nodes.length != original.length + 1) {
-        throw new IOException("Failed to add a datanode:"
-            + " nodes.length != original.length + 1, nodes="
-            + Arrays.asList(nodes) + ", original=" + Arrays.asList(original));
+        throw new IOException("Failed to add a datanode.  "
+            + "User may turn off this feature by setting "
+            + DFSConfigKeys.DFS_CLIENT_WRITE_REPLACE_DATANODE_ON_FAILURE_POLICY_KEY
+            + " in configuration, where the current policy is "
+            + dfsClient.dtpReplaceDatanodeOnFailure
+            + ".  (Nodes: current=" + Arrays.asList(nodes)
+            + ", original=" + Arrays.asList(original) + ")");
       }
       for(int i = 0; i < nodes.length; i++) {
         int j = 0;
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestReplaceDatanodeOnFailure.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestReplaceDatanodeOnFailure.java
index 31b44c447d9..86ca9ab73f0 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestReplaceDatanodeOnFailure.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestReplaceDatanodeOnFailure.java
@@ -25,6 +25,7 @@ import org.apache.commons.logging.impl.Log4JLogger;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FSDataInputStream;
 import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
@@ -234,4 +235,56 @@ public class TestReplaceDatanodeOnFailure {
       Assert.assertEquals(REPLICATION, dfsout.getNumCurrentReplicas());
     }        
   }
+
+  @Test
+  public void testAppend() throws Exception {
+    final Configuration conf = new HdfsConfiguration();
+    final short REPLICATION = (short)3;
+    
+    Assert.assertEquals(ReplaceDatanodeOnFailure.DEFAULT, ReplaceDatanodeOnFailure.get(conf));
+
+    final MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf
+        ).numDataNodes(1).build();
+
+    try {
+      final DistributedFileSystem fs = (DistributedFileSystem)cluster.getFileSystem();
+      final Path f = new Path(DIR, "testAppend");
+      
+      {
+        LOG.info("create an empty file " + f);
+        fs.create(f, REPLICATION).close();
+        final FileStatus status = fs.getFileStatus(f);
+        Assert.assertEquals(REPLICATION, status.getReplication());
+        Assert.assertEquals(0L, status.getLen());
+      }
+      
+      
+      final byte[] bytes = new byte[1000];
+      {
+        LOG.info("append " + bytes.length + " bytes to " + f);
+        final FSDataOutputStream out = fs.append(f);
+        out.write(bytes);
+        out.close();
+
+        final FileStatus status = fs.getFileStatus(f);
+        Assert.assertEquals(REPLICATION, status.getReplication());
+        Assert.assertEquals(bytes.length, status.getLen());
+      }
+
+      {
+        LOG.info("append another " + bytes.length + " bytes to " + f);
+        try {
+          final FSDataOutputStream out = fs.append(f);
+          out.write(bytes);
+          out.close();
+
+          Assert.fail();
+        } catch(IOException ioe) {
+          LOG.info("This exception is expected", ioe);
+        }
+      }
+    } finally {
+      if (cluster != null) {cluster.shutdown();}
+    }
+  }
 }