diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurableBase.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurableBase.java
index b872e772259..7521650e6fa 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurableBase.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurableBase.java
@@ -18,9 +18,18 @@
 
 package org.apache.hadoop.conf;
 
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Optional;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Maps;
 import org.apache.commons.logging.*;
+import org.apache.hadoop.util.Time;
+import org.apache.hadoop.conf.ReconfigurationUtil.PropertyChange;
 
+import java.io.IOException;
 import java.util.Collection;
+import java.util.Collections;
+import java.util.Map;
 
 /**
  * Utility base class for implementing the Reconfigurable interface.
@@ -34,6 +43,30 @@ public abstract class ReconfigurableBase
   
   private static final Log LOG =
     LogFactory.getLog(ReconfigurableBase.class);
+  // Use for testing purpose.
+  private ReconfigurationUtil reconfigurationUtil = new ReconfigurationUtil();
+
+  /** Background thread to reload configuration. */
+  private Thread reconfigThread = null;
+  private volatile boolean shouldRun = true;
+  private Object reconfigLock = new Object();
+
+  /**
+   * The timestamp when the <code>reconfigThread</code> starts.
+   */
+  private long startTime = 0;
+
+  /**
+   * The timestamp when the <code>reconfigThread</code> finishes.
+   */
+  private long endTime = 0;
+
+  /**
+   * A map of <changed property, error message>. If error message is present,
+   * it contains the messages about the error occurred when applies the particular
+   * change. Otherwise, it indicates that the change has been successfully applied.
+   */
+  private Map<PropertyChange, Optional<String>> status = null;
 
   /**
    * Construct a ReconfigurableBase.
@@ -50,6 +83,113 @@ public abstract class ReconfigurableBase
     super((conf == null) ? new Configuration() : conf);
   }
 
+  @VisibleForTesting
+  public void setReconfigurationUtil(ReconfigurationUtil ru) {
+    reconfigurationUtil = Preconditions.checkNotNull(ru);
+  }
+
+  @VisibleForTesting
+  public Collection<PropertyChange> getChangedProperties(
+      Configuration newConf, Configuration oldConf) {
+    return reconfigurationUtil.parseChangedProperties(newConf, oldConf);
+  }
+
+  /**
+   * A background thread to apply configuration changes.
+   */
+  private static class ReconfigurationThread extends Thread {
+    private ReconfigurableBase parent;
+
+    ReconfigurationThread(ReconfigurableBase base) {
+      this.parent = base;
+    }
+
+    // See {@link ReconfigurationServlet#applyChanges}
+    public void run() {
+      LOG.info("Starting reconfiguration task.");
+      Configuration oldConf = this.parent.getConf();
+      Configuration newConf = new Configuration();
+      Collection<PropertyChange> changes =
+          this.parent.getChangedProperties(newConf, oldConf);
+      Map<PropertyChange, Optional<String>> results = Maps.newHashMap();
+      for (PropertyChange change : changes) {
+        String errorMessage = null;
+        if (!this.parent.isPropertyReconfigurable(change.prop)) {
+          errorMessage = "Property " + change.prop +
+              " is not reconfigurable";
+          LOG.info(errorMessage);
+          results.put(change, Optional.of(errorMessage));
+          continue;
+        }
+        LOG.info("Change property: " + change.prop + " from \""
+            + ((change.oldVal == null) ? "<default>" : change.oldVal)
+            + "\" to \"" + ((change.newVal == null) ? "<default>" : change.newVal)
+            + "\".");
+        try {
+          this.parent.reconfigurePropertyImpl(change.prop, change.newVal);
+        } catch (ReconfigurationException e) {
+          errorMessage = e.toString();
+        }
+        results.put(change, Optional.fromNullable(errorMessage));
+      }
+
+      synchronized (this.parent.reconfigLock) {
+        this.parent.endTime = Time.monotonicNow();
+        this.parent.status = Collections.unmodifiableMap(results);
+        this.parent.reconfigThread = null;
+      }
+    }
+  }
+
+  /**
+   * Start a reconfiguration task to reload configuration in background.
+   */
+  public void startReconfigurationTask() throws IOException {
+    synchronized (reconfigLock) {
+      if (!shouldRun) {
+        String errorMessage = "The server is stopped.";
+        LOG.warn(errorMessage);
+        throw new IOException(errorMessage);
+      }
+      if (reconfigThread != null) {
+        String errorMessage = "Another reconfiguration task is running.";
+        LOG.warn(errorMessage);
+        throw new IOException(errorMessage);
+      }
+      reconfigThread = new ReconfigurationThread(this);
+      reconfigThread.setDaemon(true);
+      reconfigThread.setName("Reconfiguration Task");
+      reconfigThread.start();
+      startTime = Time.monotonicNow();
+    }
+  }
+
+  public ReconfigurationTaskStatus getReconfigurationTaskStatus() {
+    synchronized (reconfigLock) {
+      if (reconfigThread != null) {
+        return new ReconfigurationTaskStatus(startTime, 0, null);
+      }
+      return new ReconfigurationTaskStatus(startTime, endTime, status);
+    }
+  }
+
+  public void shutdownReconfigurationTask() {
+    Thread tempThread;
+    synchronized (reconfigLock) {
+      shouldRun = false;
+      if (reconfigThread == null) {
+        return;
+      }
+      tempThread = reconfigThread;
+      reconfigThread = null;
+    }
+
+    try {
+      tempThread.join();
+    } catch (InterruptedException e) {
+    }
+  }
+
   /**
    * {@inheritDoc}
    *
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurationTaskStatus.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurationTaskStatus.java
new file mode 100644
index 00000000000..a3a11cd54de
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurationTaskStatus.java
@@ -0,0 +1,70 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.conf;
+
+import com.google.common.base.Optional;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.conf.ReconfigurationUtil.PropertyChange;
+
+import java.util.Map;
+
+@InterfaceAudience.Public
+@InterfaceStability.Stable
+public class ReconfigurationTaskStatus {
+  long startTime;
+  long endTime;
+  final Map<ReconfigurationUtil.PropertyChange, Optional<String>> status;
+
+  public ReconfigurationTaskStatus(long startTime, long endTime,
+      Map<ReconfigurationUtil.PropertyChange, Optional<String>> status) {
+    this.startTime = startTime;
+    this.endTime = endTime;
+    this.status = status;
+  }
+
+  /**
+   * Return true if
+   *   - A reconfiguration task has finished or
+   *   - an active reconfiguration task is running
+   */
+  public boolean hasTask() {
+    return startTime > 0;
+  }
+
+  /**
+   * Return true if the latest reconfiguration task has finished and there is
+   * no another active task running.
+   */
+  public boolean stopped() {
+    return endTime > 0;
+  }
+
+  public long getStartTime() {
+    return startTime;
+  }
+
+  public long getEndTime() {
+    return endTime;
+  }
+
+  public final Map<PropertyChange, Optional<String>> getStatus() {
+    return status;
+  }
+}
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurationUtil.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurationUtil.java
index ca685f40584..7b107fe5c86 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurationUtil.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ReconfigurationUtil.java
@@ -63,4 +63,9 @@ public class ReconfigurationUtil {
 
     return changes.values();
   }
+
+  public Collection<PropertyChange> parseChangedProperties(
+      Configuration newConf, Configuration oldConf) {
+    return getChangedProperties(newConf, oldConf);
+  }
 }
\ No newline at end of file
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestReconfiguration.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestReconfiguration.java
index f4367523cbe..07b26eb2b82 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestReconfiguration.java
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestReconfiguration.java
@@ -18,13 +18,32 @@
 
 package org.apache.hadoop.conf;
 
+import com.google.common.base.Optional;
+import com.google.common.collect.Lists;
+import org.apache.hadoop.test.GenericTestUtils;
 import org.apache.hadoop.util.Time;
+import org.apache.hadoop.conf.ReconfigurationUtil.PropertyChange;
 import org.junit.Test;
 import org.junit.Before;
-import static org.junit.Assert.*;
 
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyString;
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.spy;
+
+import java.io.IOException;
 import java.util.Collection;
 import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CountDownLatch;
 
 public class TestReconfiguration {
   private Configuration conf1;
@@ -105,8 +124,8 @@ public class TestReconfiguration {
     }
 
     @Override
-    public synchronized void reconfigurePropertyImpl(String property, 
-                                                     String newVal) {
+    public synchronized void reconfigurePropertyImpl(
+        String property, String newVal) throws ReconfigurationException {
       // do nothing
     }
     
@@ -312,4 +331,136 @@ public class TestReconfiguration {
     
   }
 
+  private static class AsyncReconfigurableDummy extends ReconfigurableBase {
+    AsyncReconfigurableDummy(Configuration conf) {
+      super(conf);
+    }
+
+    final CountDownLatch latch = new CountDownLatch(1);
+
+    @Override
+    public Collection<String> getReconfigurableProperties() {
+      return Arrays.asList(PROP1, PROP2, PROP4);
+    }
+
+    @Override
+    public synchronized void reconfigurePropertyImpl(String property,
+        String newVal) throws ReconfigurationException {
+      try {
+        latch.await();
+      } catch (InterruptedException e) {
+        // Ignore
+      }
+    }
+  }
+
+  private static void waitAsyncReconfigureTaskFinish(ReconfigurableBase rb)
+      throws InterruptedException {
+    ReconfigurationTaskStatus status = null;
+    int count = 20;
+    while (count > 0) {
+      status = rb.getReconfigurationTaskStatus();
+      if (status.stopped()) {
+        break;
+      }
+      count--;
+      Thread.sleep(500);
+    }
+    assert(status.stopped());
+  }
+
+  @Test
+  public void testAsyncReconfigure()
+      throws ReconfigurationException, IOException, InterruptedException {
+    AsyncReconfigurableDummy dummy = spy(new AsyncReconfigurableDummy(conf1));
+
+    List<PropertyChange> changes = Lists.newArrayList();
+    changes.add(new PropertyChange("name1", "new1", "old1"));
+    changes.add(new PropertyChange("name2", "new2", "old2"));
+    changes.add(new PropertyChange("name3", "new3", "old3"));
+    doReturn(changes).when(dummy).getChangedProperties(
+        any(Configuration.class), any(Configuration.class));
+
+    doReturn(true).when(dummy).isPropertyReconfigurable(eq("name1"));
+    doReturn(false).when(dummy).isPropertyReconfigurable(eq("name2"));
+    doReturn(true).when(dummy).isPropertyReconfigurable(eq("name3"));
+
+    doNothing().when(dummy)
+        .reconfigurePropertyImpl(eq("name1"), anyString());
+    doNothing().when(dummy)
+        .reconfigurePropertyImpl(eq("name2"), anyString());
+    doThrow(new ReconfigurationException("NAME3", "NEW3", "OLD3"))
+        .when(dummy).reconfigurePropertyImpl(eq("name3"), anyString());
+
+    dummy.startReconfigurationTask();
+
+    waitAsyncReconfigureTaskFinish(dummy);
+    ReconfigurationTaskStatus status = dummy.getReconfigurationTaskStatus();
+    assertEquals(3, status.getStatus().size());
+    for (Map.Entry<PropertyChange, Optional<String>> result :
+        status.getStatus().entrySet()) {
+      PropertyChange change = result.getKey();
+      if (change.prop.equals("name1")) {
+        assertFalse(result.getValue().isPresent());
+      } else if (change.prop.equals("name2")) {
+        assertThat(result.getValue().get(),
+            containsString("Property name2 is not reconfigurable"));
+      } else if (change.prop.equals("name3")) {
+        assertThat(result.getValue().get(), containsString("NAME3"));
+      } else {
+        fail("Unknown property: " + change.prop);
+      }
+    }
+  }
+
+  @Test(timeout=30000)
+  public void testStartReconfigurationFailureDueToExistingRunningTask()
+      throws InterruptedException, IOException {
+    AsyncReconfigurableDummy dummy = spy(new AsyncReconfigurableDummy(conf1));
+    List<PropertyChange> changes = Lists.newArrayList(
+        new PropertyChange(PROP1, "new1", "old1")
+    );
+    doReturn(changes).when(dummy).getChangedProperties(
+        any(Configuration.class), any(Configuration.class));
+
+    ReconfigurationTaskStatus status = dummy.getReconfigurationTaskStatus();
+    assertFalse(status.hasTask());
+
+    dummy.startReconfigurationTask();
+    status = dummy.getReconfigurationTaskStatus();
+    assertTrue(status.hasTask());
+    assertFalse(status.stopped());
+
+    // An active reconfiguration task is running.
+    try {
+      dummy.startReconfigurationTask();
+      fail("Expect to throw IOException.");
+    } catch (IOException e) {
+      GenericTestUtils.assertExceptionContains(
+          "Another reconfiguration task is running", e);
+    }
+    status = dummy.getReconfigurationTaskStatus();
+    assertTrue(status.hasTask());
+    assertFalse(status.stopped());
+
+    dummy.latch.countDown();
+    waitAsyncReconfigureTaskFinish(dummy);
+    status = dummy.getReconfigurationTaskStatus();
+    assertTrue(status.hasTask());
+    assertTrue(status.stopped());
+
+    // The first task has finished.
+    dummy.startReconfigurationTask();
+    waitAsyncReconfigureTaskFinish(dummy);
+    ReconfigurationTaskStatus status2 = dummy.getReconfigurationTaskStatus();
+    assertTrue(status2.getStartTime() >= status.getEndTime());
+
+    dummy.shutdownReconfigurationTask();
+    try {
+      dummy.startReconfigurationTask();
+      fail("Expect to throw IOException");
+    } catch (IOException e) {
+      GenericTestUtils.assertExceptionContains("The server is stopped", e);
+    }
+  }
 }
\ No newline at end of file
diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 4b6b0db5df3..487a5470799 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -585,6 +585,9 @@ Release 2.6.0 - UNRELEASED
     HDFS-7118. Improve diagnostics on storage directory rename operations by
     using NativeIO#renameTo in Storage#rename. (cnauroth)
 
+    HDFS-6808. Add command line option to ask DataNode reload configuration.
+    (Lei Xu via Colin Patrick McCabe)
+
   OPTIMIZATIONS
 
     HDFS-6690. Deduplicate xattr names in memory. (wang)
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientDatanodeProtocol.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientDatanodeProtocol.java
index 475686572f0..3a247350d7e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientDatanodeProtocol.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientDatanodeProtocol.java
@@ -22,6 +22,7 @@ import java.util.List;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.conf.ReconfigurationTaskStatus;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
 import org.apache.hadoop.hdfs.security.token.block.BlockTokenSelector;
@@ -144,4 +145,15 @@ public interface ClientDatanodeProtocol {
    * @return software/config version and uptime of the datanode
    */
   DatanodeLocalInfo getDatanodeInfo() throws IOException;
+
+  /**
+   * Asynchronously reload configuration on disk and apply changes.
+   */
+  void startReconfiguration() throws IOException;
+
+  /**
+   * Get the status of the previously issued reconfig task.
+   * @see {@link org.apache.hadoop.conf.ReconfigurationTaskStatus}.
+   */
+  ReconfigurationTaskStatus getReconfigurationStatus() throws IOException;
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolServerSideTranslatorPB.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolServerSideTranslatorPB.java
index c8fa2fed66a..ed7f0ae160c 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolServerSideTranslatorPB.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolServerSideTranslatorPB.java
@@ -20,11 +20,14 @@ package org.apache.hadoop.hdfs.protocolPB;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Map;
 
+import com.google.common.base.Optional;
 import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.ReconfigurationTaskStatus;
+import org.apache.hadoop.conf.ReconfigurationUtil.PropertyChange;
 import org.apache.hadoop.hdfs.protocol.BlockLocalPathInfo;
 import org.apache.hadoop.hdfs.protocol.ClientDatanodeProtocol;
-import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
 import org.apache.hadoop.hdfs.protocol.HdfsBlocksMetadata;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.DeleteBlockPoolRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.DeleteBlockPoolResponseProto;
@@ -32,6 +35,9 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetBlo
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetBlockLocalPathInfoResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetDatanodeInfoRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetDatanodeInfoResponseProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetReconfigurationStatusConfigChangeProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetReconfigurationStatusRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetReconfigurationStatusResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetHdfsBlockLocationsRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetHdfsBlockLocationsResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetHdfsBlockLocationsResponseProto.Builder;
@@ -41,11 +47,11 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.Refres
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.RefreshNamenodesResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.ShutdownDatanodeRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.ShutdownDatanodeResponseProto;
-import org.apache.hadoop.hdfs.protocol.proto.HdfsProtos.ExtendedBlockProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.StartReconfigurationRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.StartReconfigurationResponseProto;
 import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
 import org.apache.hadoop.security.proto.SecurityProtos.TokenProto;
 import org.apache.hadoop.security.token.Token;
-import org.apache.hadoop.util.VersionInfo;
 
 import com.google.common.primitives.Longs;
 import com.google.protobuf.ByteString;
@@ -66,6 +72,8 @@ public class ClientDatanodeProtocolServerSideTranslatorPB implements
       DeleteBlockPoolResponseProto.newBuilder().build();
   private final static ShutdownDatanodeResponseProto SHUTDOWN_DATANODE_RESP =
       ShutdownDatanodeResponseProto.newBuilder().build();
+  private final static StartReconfigurationResponseProto START_RECONFIG_RESP =
+      StartReconfigurationResponseProto.newBuilder().build();
   
   private final ClientDatanodeProtocol impl;
 
@@ -182,4 +190,51 @@ public class ClientDatanodeProtocolServerSideTranslatorPB implements
     }
     return res;
   }
+
+  @Override
+  public StartReconfigurationResponseProto startReconfiguration(
+      RpcController unused, StartReconfigurationRequestProto request)
+    throws ServiceException {
+    try {
+      impl.startReconfiguration();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+    return START_RECONFIG_RESP;
+  }
+
+  @Override
+  public GetReconfigurationStatusResponseProto getReconfigurationStatus(
+      RpcController unused, GetReconfigurationStatusRequestProto request)
+      throws ServiceException {
+    GetReconfigurationStatusResponseProto.Builder builder =
+        GetReconfigurationStatusResponseProto.newBuilder();
+    try {
+      ReconfigurationTaskStatus status = impl.getReconfigurationStatus();
+      builder.setStartTime(status.getStartTime());
+      if (status.stopped()) {
+        builder.setEndTime(status.getEndTime());
+        assert status.getStatus() != null;
+        for (Map.Entry<PropertyChange, Optional<String>> result :
+            status.getStatus().entrySet()) {
+          GetReconfigurationStatusConfigChangeProto.Builder changeBuilder =
+              GetReconfigurationStatusConfigChangeProto.newBuilder();
+          PropertyChange change = result.getKey();
+          changeBuilder.setName(change.prop);
+          changeBuilder.setOldValue(change.oldVal != null ? change.oldVal : "");
+          if (change.newVal != null) {
+            changeBuilder.setNewValue(change.newVal);
+          }
+          if (result.getValue().isPresent()) {
+            // Get full stack trace.
+            changeBuilder.setErrorMessage(result.getValue().get());
+          }
+          builder.addChanges(changeBuilder);
+        }
+      }
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+    return builder.build();
+  }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolTranslatorPB.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolTranslatorPB.java
index ca152b3a83a..00b6ad745ff 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolTranslatorPB.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolTranslatorPB.java
@@ -21,16 +21,20 @@ import java.io.Closeable;
 import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
 
 import javax.net.SocketFactory;
 
+import com.google.common.base.Optional;
+import com.google.common.collect.Maps;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.conf.ReconfigurationTaskStatus;
+import org.apache.hadoop.conf.ReconfigurationUtil.PropertyChange;
 import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
 import org.apache.hadoop.hdfs.protocol.BlockLocalPathInfo;
 import org.apache.hadoop.hdfs.protocol.ClientDatanodeProtocol;
@@ -48,8 +52,11 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetHdf
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetHdfsBlockLocationsResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetReplicaVisibleLengthRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.RefreshNamenodesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetReconfigurationStatusRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetReconfigurationStatusResponseProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.GetReconfigurationStatusConfigChangeProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.ShutdownDatanodeRequestProto;
-import org.apache.hadoop.hdfs.protocol.proto.HdfsProtos.ExtendedBlockProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos.StartReconfigurationRequestProto;
 import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
 import org.apache.hadoop.ipc.ProtobufHelper;
 import org.apache.hadoop.ipc.ProtobufRpcEngine;
@@ -87,6 +94,10 @@ public class ClientDatanodeProtocolTranslatorPB implements
       RefreshNamenodesRequestProto.newBuilder().build();
   private final static GetDatanodeInfoRequestProto VOID_GET_DATANODE_INFO =
       GetDatanodeInfoRequestProto.newBuilder().build();
+  private final static GetReconfigurationStatusRequestProto VOID_GET_RECONFIG_STATUS =
+      GetReconfigurationStatusRequestProto.newBuilder().build();
+  private final static StartReconfigurationRequestProto VOID_START_RECONFIG =
+      StartReconfigurationRequestProto.newBuilder().build();
 
   public ClientDatanodeProtocolTranslatorPB(DatanodeID datanodeid,
       Configuration conf, int socketTimeout, boolean connectToDnViaHostname,
@@ -282,4 +293,44 @@ public class ClientDatanodeProtocolTranslatorPB implements
     }
   }
 
+  @Override
+  public void startReconfiguration() throws IOException {
+    try {
+      rpcProxy.startReconfiguration(NULL_CONTROLLER, VOID_START_RECONFIG);
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  @Override
+  public ReconfigurationTaskStatus getReconfigurationStatus() throws IOException {
+    GetReconfigurationStatusResponseProto response;
+    Map<PropertyChange, Optional<String>> statusMap = null;
+    long startTime;
+    long endTime = 0;
+    try {
+      response = rpcProxy.getReconfigurationStatus(NULL_CONTROLLER,
+          VOID_GET_RECONFIG_STATUS);
+      startTime = response.getStartTime();
+      if (response.hasEndTime()) {
+        endTime = response.getEndTime();
+      }
+      if (response.getChangesCount() > 0) {
+        statusMap = Maps.newHashMap();
+        for (GetReconfigurationStatusConfigChangeProto change :
+            response.getChangesList()) {
+          PropertyChange pc = new PropertyChange(
+              change.getName(), change.getNewValue(), change.getOldValue());
+          String errorMessage = null;
+          if (change.hasErrorMessage()) {
+            errorMessage = change.getErrorMessage();
+          }
+          statusMap.put(pc, Optional.fromNullable(errorMessage));
+        }
+      }
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+    return new ReconfigurationTaskStatus(startTime, endTime, statusMap);
+  }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java
index b1ef18673ae..44e471e8aa5 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java
@@ -90,6 +90,7 @@ import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.conf.ReconfigurableBase;
 import org.apache.hadoop.conf.ReconfigurationException;
+import org.apache.hadoop.conf.ReconfigurationTaskStatus;
 import org.apache.hadoop.fs.CommonConfigurationKeys;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.LocalFileSystem;
@@ -336,6 +337,21 @@ public class DataNode extends ReconfigurableBase
 
   private SpanReceiverHost spanReceiverHost;
 
+  /**
+   * Creates a dummy DataNode for testing purpose.
+   */
+  @VisibleForTesting
+  @InterfaceAudience.LimitedPrivate("HDFS")
+  DataNode(final Configuration conf) {
+    super(conf);
+    this.fileDescriptorPassingDisabledReason = null;
+    this.maxNumberOfBlocksToLog = 0;
+    this.confVersion = null;
+    this.usersWithLocalPathAccess = null;
+    this.connectToDnViaHostname = false;
+    this.getHdfsBlockLocationsEnabled = false;
+  }
+
   /**
    * Create the DataNode given a configuration, an array of dataDirs,
    * and a namenode proxy
@@ -478,7 +494,6 @@ public class DataNode extends ReconfigurableBase
    */
   private synchronized void refreshVolumes(String newVolumes) throws Exception {
     Configuration conf = getConf();
-    String oldVolumes = conf.get(DFS_DATANODE_DATA_DIR_KEY);
     conf.set(DFS_DATANODE_DATA_DIR_KEY, newVolumes);
     List<StorageLocation> locations = getStorageLocations(conf);
 
@@ -486,6 +501,7 @@ public class DataNode extends ReconfigurableBase
     dataDirs = locations;
     ChangedVolumes changedVolumes = parseChangedVolumes();
 
+    StringBuilder errorMessageBuilder = new StringBuilder();
     try {
       if (numOldDataDirs + changedVolumes.newLocations.size() -
           changedVolumes.deactivateLocations.size() <= 0) {
@@ -514,8 +530,13 @@ public class DataNode extends ReconfigurableBase
           // Clean all failed volumes.
           for (StorageLocation location : changedVolumes.newLocations) {
             if (!succeedVolumes.contains(location)) {
+              errorMessageBuilder.append("FAILED TO ADD:");
               failedVolumes.add(location);
+            } else {
+              errorMessageBuilder.append("ADDED:");
             }
+            errorMessageBuilder.append(location);
+            errorMessageBuilder.append("\n");
           }
           storage.removeVolumes(failedVolumes);
           data.removeVolumes(failedVolumes);
@@ -529,10 +550,12 @@ public class DataNode extends ReconfigurableBase
         data.removeVolumes(changedVolumes.deactivateLocations);
         storage.removeVolumes(changedVolumes.deactivateLocations);
       }
+
+      if (errorMessageBuilder.length() > 0) {
+        throw new IOException(errorMessageBuilder.toString());
+      }
     } catch (IOException e) {
-      LOG.warn("There is IOException when refreshing volumes! "
-          + "Recover configurations: " + DFS_DATANODE_DATA_DIR_KEY
-          + " = " + oldVolumes, e);
+      LOG.warn("There is IOException when refresh volumes! ", e);
       throw e;
     }
   }
@@ -1594,6 +1617,9 @@ public class DataNode extends ReconfigurableBase
     // before the restart prep is done.
     this.shouldRun = false;
     
+    // wait reconfiguration thread, if any, to exit
+    shutdownReconfigurationTask();
+
     // wait for all data receiver threads to exit
     if (this.threadGroup != null) {
       int sleepMs = 2;
@@ -2847,6 +2873,18 @@ public class DataNode extends ReconfigurableBase
         confVersion, uptime);
   }
 
+  @Override // ClientDatanodeProtocol
+  public void startReconfiguration() throws IOException {
+    checkSuperuserPrivilege();
+    startReconfigurationTask();
+  }
+
+  @Override // ClientDatanodeProtocol
+  public ReconfigurationTaskStatus getReconfigurationStatus() throws IOException {
+    checkSuperuserPrivilege();
+    return getReconfigurationTaskStatus();
+  }
+
   /**
    * @param addr rpc address of the namenode
    * @return true if the datanode is connected to a NameNode at the
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSAdmin.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSAdmin.java
index 525f6d3e25d..298564e41a8 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSAdmin.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSAdmin.java
@@ -29,14 +29,19 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Date;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.TreeSet;
 
+import com.google.common.base.Optional;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.conf.ReconfigurationTaskStatus;
+import org.apache.hadoop.conf.ReconfigurationUtil.PropertyChange;
 import org.apache.hadoop.fs.CommonConfigurationKeys;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.FsShell;
@@ -378,6 +383,7 @@ public class DFSAdmin extends FsShell {
     "\t[-refreshSuperUserGroupsConfiguration]\n" +
     "\t[-refreshCallQueue]\n" +
     "\t[-refresh <host:ipc_port> <key> [arg1..argn]\n" +
+    "\t[-reconfig <datanode|...> <host:ipc_port> <start|status>]\n" +
     "\t[-printTopology]\n" +
     "\t[-refreshNamenodes datanode_host:ipc_port]\n"+
     "\t[-deleteBlockPool datanode_host:ipc_port blockpoolId [force]]\n"+
@@ -915,9 +921,14 @@ public class DFSAdmin extends FsShell {
 
     String refreshCallQueue = "-refreshCallQueue: Reload the call queue from config\n";
 
+    String reconfig = "-reconfig <datanode|...> <host:ipc_port> <start|status>:\n" +
+        "\tStarts reconfiguration or gets the status of an ongoing reconfiguration.\n" +
+        "\tThe second parameter specifies the node type.\n" +
+        "\tCurrently, only reloading DataNode's configuration is supported.\n";
+
     String genericRefresh = "-refresh: Arguments are <hostname:port> <resource_identifier> [arg1..argn]\n" +
       "\tTriggers a runtime-refresh of the resource specified by <resource_identifier>\n" +
-      "\ton <hostname:port>. All other args after are sent to the host.";
+      "\ton <hostname:port>. All other args after are sent to the host.\n";
 
     String printTopology = "-printTopology: Print a tree of the racks and their\n" +
                            "\t\tnodes as reported by the Namenode\n";
@@ -1011,6 +1022,8 @@ public class DFSAdmin extends FsShell {
       System.out.println(refreshCallQueue);
     } else if ("refresh".equals(cmd)) {
       System.out.println(genericRefresh);
+    } else if ("reconfig".equals(cmd)) {
+      System.out.println(reconfig);
     } else if ("printTopology".equals(cmd)) {
       System.out.println(printTopology);
     } else if ("refreshNamenodes".equals(cmd)) {
@@ -1055,6 +1068,7 @@ public class DFSAdmin extends FsShell {
       System.out.println(refreshSuperUserGroupsConfiguration);
       System.out.println(refreshCallQueue);
       System.out.println(genericRefresh);
+      System.out.println(reconfig);
       System.out.println(printTopology);
       System.out.println(refreshNamenodes);
       System.out.println(deleteBlockPool);
@@ -1364,6 +1378,75 @@ public class DFSAdmin extends FsShell {
     return 0;
   }
 
+  public int reconfig(String[] argv, int i) throws IOException {
+    String nodeType = argv[i];
+    String address = argv[i + 1];
+    String op = argv[i + 2];
+    if ("start".equals(op)) {
+      return startReconfiguration(nodeType, address);
+    } else if ("status".equals(op)) {
+      return getReconfigurationStatus(nodeType, address, System.out, System.err);
+    }
+    System.err.println("Unknown operation: " + op);
+    return -1;
+  }
+
+  int startReconfiguration(String nodeType, String address) throws IOException {
+    if ("datanode".equals(nodeType)) {
+      ClientDatanodeProtocol dnProxy = getDataNodeProxy(address);
+      dnProxy.startReconfiguration();
+      System.out.println("Started reconfiguration task on DataNode " + address);
+    } else {
+      System.err.println("Node type " + nodeType +
+          " does not support reconfiguration.");
+    }
+    return -1;
+  }
+
+  int getReconfigurationStatus(String nodeType, String address,
+      PrintStream out, PrintStream err) throws IOException {
+    if ("datanode".equals(nodeType)) {
+      ClientDatanodeProtocol dnProxy = getDataNodeProxy(address);
+      try {
+        ReconfigurationTaskStatus status = dnProxy.getReconfigurationStatus();
+        out.print("Reconfiguring status for DataNode[" + address + "]: ");
+        if (!status.hasTask()) {
+          out.println("no task was found.");
+          return 0;
+        }
+        out.print("started at " + new Date(status.getStartTime()));
+        if (!status.stopped()) {
+          out.println(" and is still running.");
+          return 0;
+        }
+
+        out.println(" and finished at " +
+            new Date(status.getEndTime()).toString() + ".");
+        for (Map.Entry<PropertyChange, Optional<String>> result :
+            status.getStatus().entrySet()) {
+          if (!result.getValue().isPresent()) {
+            out.print("SUCCESS: ");
+          } else {
+            out.print("FAILED: ");
+          }
+          out.printf("Change property %s\n\tFrom: \"%s\"\n\tTo: \"%s\"\n",
+              result.getKey().prop, result.getKey().oldVal,
+              result.getKey().newVal);
+          if (result.getValue().isPresent()) {
+            out.println("\tError: " + result.getValue().get() + ".");
+          }
+        }
+      } catch (IOException e) {
+        err.println("DataNode reloading configuration: " + e + ".");
+        return -1;
+      }
+    } else {
+      err.println("Node type " + nodeType + " does not support reconfiguration.");
+      return -1;
+    }
+    return 0;
+  }
+
   public int genericRefresh(String[] argv, int i) throws IOException {
     String hostport = argv[i++];
     String identifier = argv[i++];
@@ -1482,6 +1565,9 @@ public class DFSAdmin extends FsShell {
     } else if ("-refreshCallQueue".equals(cmd)) {
       System.err.println("Usage: hdfs dfsadmin"
                          + " [-refreshCallQueue]");
+    } else if ("-reconfig".equals(cmd)) {
+      System.err.println("Usage: java DFSAdmin"
+                         + " [-reconfig <datanode|...> <host:port> <start|status>]");
     } else if ("-refresh".equals(cmd)) {
       System.err.println("Usage: hdfs dfsadmin"
                          + " [-refresh <hostname:port> <resource_identifier> [arg1..argn]");
@@ -1614,6 +1700,11 @@ public class DFSAdmin extends FsShell {
         printUsage(cmd);
         return exitCode;
       }
+    } else if ("-reconfig".equals(cmd)) {
+      if (argv.length != 4) {
+        printUsage(cmd);
+        return exitCode;
+      }
     } else if ("-deleteBlockPool".equals(cmd)) {
       if ((argv.length != 3) && (argv.length != 4)) {
         printUsage(cmd);
@@ -1720,6 +1811,8 @@ public class DFSAdmin extends FsShell {
         exitCode = shutdownDatanode(argv, i);
       } else if ("-getDatanodeInfo".equals(cmd)) {
         exitCode = getDatanodeInfo(argv, i);
+      } else if ("-reconfig".equals(cmd)) {
+        exitCode = reconfig(argv, i);
       } else if ("-setStoragePolicy".equals(cmd)) {
         exitCode = setStoragePolicy(argv);
       } else if ("-getStoragePolicy".equals(cmd)) {
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/ClientDatanodeProtocol.proto b/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/ClientDatanodeProtocol.proto
index 8779f7c3580..61f787bec92 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/ClientDatanodeProtocol.proto
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/ClientDatanodeProtocol.proto
@@ -149,6 +149,30 @@ message GetDatanodeInfoResponseProto {
   required DatanodeLocalInfoProto localInfo = 1;
 }
 
+/** Asks DataNode to reload configuration file. */
+message StartReconfigurationRequestProto {
+}
+
+message StartReconfigurationResponseProto {
+}
+
+/** Query the running status of reconfiguration process */
+message GetReconfigurationStatusRequestProto {
+}
+
+message GetReconfigurationStatusConfigChangeProto {
+  required string name = 1;
+  required string oldValue = 2;
+  optional string newValue = 3;
+  optional string errorMessage = 4;  // It is empty if success.
+}
+
+message GetReconfigurationStatusResponseProto {
+  required int64 startTime = 1;
+  optional int64 endTime = 2;
+  repeated GetReconfigurationStatusConfigChangeProto changes = 3;
+}
+
 /**
  * Protocol used from client to the Datanode.
  * See the request and response for details of rpc call.
@@ -192,4 +216,10 @@ service ClientDatanodeProtocolService {
 
   rpc getDatanodeInfo(GetDatanodeInfoRequestProto)
       returns(GetDatanodeInfoResponseProto);
+
+  rpc getReconfigurationStatus(GetReconfigurationStatusRequestProto)
+      returns(GetReconfigurationStatusResponseProto);
+
+  rpc startReconfiguration(StartReconfigurationRequestProto)
+      returns(StartReconfigurationResponseProto);
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/tools/TestDFSAdmin.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/tools/TestDFSAdmin.java
new file mode 100644
index 00000000000..35c61f0255f
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/tools/TestDFSAdmin.java
@@ -0,0 +1,152 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.tools;
+
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_DATANODE_DATA_DIR_KEY;
+
+import com.google.common.collect.Lists;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.conf.ReconfigurationUtil;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.server.common.Storage;
+import org.apache.hadoop.hdfs.server.datanode.DataNode;
+import org.apache.hadoop.hdfs.server.datanode.StorageLocation;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.io.PrintStream;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Scanner;
+
+import static org.hamcrest.CoreMatchers.allOf;
+import static org.hamcrest.CoreMatchers.anyOf;
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.not;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class TestDFSAdmin {
+  private MiniDFSCluster cluster;
+  private DFSAdmin admin;
+  private DataNode datanode;
+
+  @Before
+  public void setUp() throws Exception {
+    Configuration conf = new Configuration();
+    cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
+    cluster.waitActive();
+
+    admin = new DFSAdmin();
+    datanode = cluster.getDataNodes().get(0);
+  }
+
+  @After
+  public void tearDown() throws Exception {
+    if (cluster != null) {
+      cluster.shutdown();
+      cluster = null;
+    }
+  }
+
+  private List<String> getReconfigureStatus(String nodeType, String address)
+      throws IOException {
+    ByteArrayOutputStream bufOut = new ByteArrayOutputStream();
+    PrintStream out = new PrintStream(bufOut);
+    ByteArrayOutputStream bufErr = new ByteArrayOutputStream();
+    PrintStream err = new PrintStream(bufErr);
+    admin.getReconfigurationStatus(nodeType, address, out, err);
+    Scanner scanner = new Scanner(bufOut.toString());
+    List<String> outputs = Lists.newArrayList();
+    while (scanner.hasNextLine()) {
+      outputs.add(scanner.nextLine());
+    }
+    return outputs;
+  }
+
+  @Test(timeout = 30000)
+  public void testGetReconfigureStatus()
+      throws IOException, InterruptedException {
+    ReconfigurationUtil ru = mock(ReconfigurationUtil.class);
+    datanode.setReconfigurationUtil(ru);
+
+    List<ReconfigurationUtil.PropertyChange> changes =
+        new ArrayList<ReconfigurationUtil.PropertyChange>();
+    File newDir = new File(cluster.getDataDirectory(), "data_new");
+    newDir.mkdirs();
+    changes.add(new ReconfigurationUtil.PropertyChange(
+        DFS_DATANODE_DATA_DIR_KEY, newDir.toString(),
+        datanode.getConf().get(DFS_DATANODE_DATA_DIR_KEY)));
+    changes.add(new ReconfigurationUtil.PropertyChange(
+        "randomKey", "new123", "old456"));
+    when(ru.parseChangedProperties(any(Configuration.class),
+        any(Configuration.class))).thenReturn(changes);
+
+    final int port = datanode.getIpcPort();
+    final String address = "localhost:" + port;
+
+    admin.startReconfiguration("datanode", address);
+
+    List<String> outputs = null;
+    int count = 100;
+    while (count > 0) {
+      outputs = getReconfigureStatus("datanode", address);
+      if (!outputs.isEmpty() && outputs.get(0).contains("finished")) {
+        break;
+      }
+      count--;
+      Thread.sleep(100);
+    }
+    assertTrue(count > 0);
+    assertThat(outputs.size(), is(8));  // 3 (SUCCESS) + 4 (FAILED)
+
+    List<StorageLocation> locations = DataNode.getStorageLocations(
+        datanode.getConf());
+    assertThat(locations.size(), is(1));
+    assertThat(locations.get(0).getFile(), is(newDir));
+    // Verify the directory is appropriately formatted.
+    assertTrue(new File(newDir, Storage.STORAGE_DIR_CURRENT).isDirectory());
+
+    int successOffset = outputs.get(1).startsWith("SUCCESS:") ? 1 : 5;
+    int failedOffset = outputs.get(1).startsWith("FAILED:") ? 1: 4;
+    assertThat(outputs.get(successOffset),
+        containsString("Change property " + DFS_DATANODE_DATA_DIR_KEY));
+    assertThat(outputs.get(successOffset + 1),
+        is(allOf(containsString("From:"), containsString("data1"),
+            containsString("data2"))));
+    assertThat(outputs.get(successOffset + 2),
+        is(not(anyOf(containsString("data1"), containsString("data2")))));
+    assertThat(outputs.get(successOffset + 2),
+        is(allOf(containsString("To"), containsString("data_new"))));
+    assertThat(outputs.get(failedOffset),
+        containsString("Change property randomKey"));
+    assertThat(outputs.get(failedOffset + 1),
+        containsString("From: \"old456\""));
+    assertThat(outputs.get(failedOffset + 2),
+        containsString("To: \"new123\""));
+  }
+}
\ No newline at end of file