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From cmcc...@apache.org
Subject hadoop git commit: HDFS-7758. Retire FsDatasetSpi#getVolumes() and use FsDatasetSpi#getVolumeRefs() instead (Lei (Eddy) Xu via Colin P. McCabe)
Date Tue, 05 May 2015 18:09:07 GMT
Repository: hadoop
Updated Branches:
  refs/heads/trunk 3ff91e9e9 -> 24d3a2d4f


HDFS-7758. Retire FsDatasetSpi#getVolumes() and use FsDatasetSpi#getVolumeRefs() instead (Lei (Eddy) Xu via Colin P. McCabe)


Project: http://git-wip-us.apache.org/repos/asf/hadoop/repo
Commit: http://git-wip-us.apache.org/repos/asf/hadoop/commit/24d3a2d4
Tree: http://git-wip-us.apache.org/repos/asf/hadoop/tree/24d3a2d4
Diff: http://git-wip-us.apache.org/repos/asf/hadoop/diff/24d3a2d4

Branch: refs/heads/trunk
Commit: 24d3a2d4fdd836ac9a5bc755a7fb9354f7a582b1
Parents: 3ff91e9
Author: Colin Patrick Mccabe <cmccabe@cloudera.com>
Authored: Tue May 5 10:55:04 2015 -0700
Committer: Colin Patrick Mccabe <cmccabe@cloudera.com>
Committed: Tue May 5 11:08:59 2015 -0700

----------------------------------------------------------------------
 hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt     |   3 +
 .../hdfs/server/datanode/DirectoryScanner.java  |  69 +++++-----
 .../server/datanode/fsdataset/FsDatasetSpi.java |  99 +++++++++++++-
 .../datanode/fsdataset/FsVolumeReference.java   |  13 +-
 .../datanode/fsdataset/impl/FsDatasetImpl.java  |  29 ++---
 .../datanode/fsdataset/impl/FsVolumeImpl.java   |   7 +-
 .../datanode/fsdataset/impl/FsVolumeList.java   |   7 +-
 .../org/apache/hadoop/hdfs/MiniDFSCluster.java  |  23 ++--
 .../hdfs/MiniDFSClusterWithNodeGroup.java       |  17 +--
 .../TestNameNodePrunesMissingStorages.java      |  18 +--
 .../server/datanode/SimulatedFSDataset.java     |   2 +-
 .../TestBlockHasMultipleReplicasOnSameDN.java   |  14 +-
 .../hdfs/server/datanode/TestBlockScanner.java  |   8 +-
 .../datanode/TestDataNodeHotSwapVolumes.java    |  21 ++-
 .../datanode/TestDataNodeVolumeFailure.java     |   9 +-
 .../server/datanode/TestDirectoryScanner.java   | 130 +++++++++++--------
 .../hdfs/server/datanode/TestDiskError.java     |  12 +-
 .../datanode/TestIncrementalBlockReports.java   |   6 +-
 .../datanode/TestIncrementalBrVariations.java   |  81 ++++++------
 .../server/datanode/TestTriggerBlockReport.java |   8 +-
 .../extdataset/ExternalDatasetImpl.java         |   2 +-
 .../fsdataset/impl/LazyPersistTestCase.java     |  72 +++++-----
 .../fsdataset/impl/TestDatanodeRestart.java     |  20 ++-
 .../fsdataset/impl/TestFsDatasetImpl.java       |  39 ++++--
 .../fsdataset/impl/TestFsVolumeList.java        |   9 +-
 .../fsdataset/impl/TestRbwSpaceReservation.java |  43 +++---
 .../fsdataset/impl/TestWriteToReplica.java      |  70 ++++++----
 .../hdfs/server/mover/TestStorageMover.java     |  19 ++-
 28 files changed, 515 insertions(+), 335 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 08ab7e7..c89e6fe 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -507,6 +507,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-8237. Move all protocol classes used by ClientProtocol to hdfs-client.
     (wheat9)
 
+    HDFS-7758. Retire FsDatasetSpi#getVolumes() and use
+    FsDatasetSpi#getVolumeRefs() instead (Lei (Eddy) Xu via Colin P. McCabe)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DirectoryScanner.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DirectoryScanner.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DirectoryScanner.java
index 62885a9..8453094 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DirectoryScanner.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DirectoryScanner.java
@@ -527,59 +527,48 @@ public class DirectoryScanner implements Runnable {
     diffRecord.add(new ScanInfo(blockId, null, null, vol));
   }
 
-  /** Is the given volume still valid in the dataset? */
-  private static boolean isValid(final FsDatasetSpi<?> dataset,
-      final FsVolumeSpi volume) {
-    for (FsVolumeSpi vol : dataset.getVolumes()) {
-      if (vol == volume) {
-        return true;
-      }
-    }
-    return false;
-  }
-
   /** Get lists of blocks on the disk sorted by blockId, per blockpool */
   private Map<String, ScanInfo[]> getDiskReport() {
+    ScanInfoPerBlockPool list = new ScanInfoPerBlockPool();
+    ScanInfoPerBlockPool[] dirReports = null;
     // First get list of data directories
-    final List<? extends FsVolumeSpi> volumes = dataset.getVolumes();
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+        dataset.getFsVolumeReferences()) {
 
-    // Use an array since the threads may return out of order and
-    // compilersInProgress#keySet may return out of order as well.
-    ScanInfoPerBlockPool[] dirReports = new ScanInfoPerBlockPool[volumes.size()];
+      // Use an array since the threads may return out of order and
+      // compilersInProgress#keySet may return out of order as well.
+      dirReports = new ScanInfoPerBlockPool[volumes.size()];
 
-    Map<Integer, Future<ScanInfoPerBlockPool>> compilersInProgress =
-      new HashMap<Integer, Future<ScanInfoPerBlockPool>>();
+      Map<Integer, Future<ScanInfoPerBlockPool>> compilersInProgress =
+          new HashMap<Integer, Future<ScanInfoPerBlockPool>>();
 
-    for (int i = 0; i < volumes.size(); i++) {
-      if (isValid(dataset, volumes.get(i))) {
+      for (int i = 0; i < volumes.size(); i++) {
         ReportCompiler reportCompiler =
-          new ReportCompiler(datanode,volumes.get(i));
-        Future<ScanInfoPerBlockPool> result = 
-          reportCompileThreadPool.submit(reportCompiler);
+            new ReportCompiler(datanode, volumes.get(i));
+        Future<ScanInfoPerBlockPool> result =
+            reportCompileThreadPool.submit(reportCompiler);
         compilersInProgress.put(i, result);
       }
-    }
-    
-    for (Entry<Integer, Future<ScanInfoPerBlockPool>> report :
-        compilersInProgress.entrySet()) {
-      try {
-        dirReports[report.getKey()] = report.getValue().get();
-      } catch (Exception ex) {
-        LOG.error("Error compiling report", ex);
-        // Propagate ex to DataBlockScanner to deal with
-        throw new RuntimeException(ex);
+
+      for (Entry<Integer, Future<ScanInfoPerBlockPool>> report :
+          compilersInProgress.entrySet()) {
+        try {
+          dirReports[report.getKey()] = report.getValue().get();
+        } catch (Exception ex) {
+          LOG.error("Error compiling report", ex);
+          // Propagate ex to DataBlockScanner to deal with
+          throw new RuntimeException(ex);
+        }
       }
+    } catch (IOException e) {
+      LOG.error("Unexpected IOException by closing FsVolumeReference", e);
     }
-
-    // Compile consolidated report for all the volumes
-    ScanInfoPerBlockPool list = new ScanInfoPerBlockPool();
-    for (int i = 0; i < volumes.size(); i++) {
-      if (isValid(dataset, volumes.get(i))) {
-        // volume is still valid
-        list.addAll(dirReports[i]);
+    if (dirReports != null) {
+      // Compile consolidated report for all the volumes
+      for (ScanInfoPerBlockPool report : dirReports) {
+        list.addAll(report);
       }
     }
-
     return list.toSortedArrays();
   }
 

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsDatasetSpi.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsDatasetSpi.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsDatasetSpi.java
index 8a741de..76c4f02 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsDatasetSpi.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsDatasetSpi.java
@@ -18,13 +18,16 @@
 package org.apache.hadoop.hdfs.server.datanode.fsdataset;
 
 
+import java.io.Closeable;
 import java.io.EOFException;
 import java.io.File;
 import java.io.FileDescriptor;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
-import java.util.Collection;
+import java.nio.channels.ClosedChannelException;
+import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -50,7 +53,6 @@ import org.apache.hadoop.hdfs.server.datanode.ReplicaNotFoundException;
 import org.apache.hadoop.hdfs.server.datanode.StorageLocation;
 import org.apache.hadoop.hdfs.server.datanode.UnexpectedReplicaStateException;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetFactory;
-import org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl;
 import org.apache.hadoop.hdfs.server.datanode.metrics.FSDatasetMBean;
 import org.apache.hadoop.hdfs.server.protocol.BlockRecoveryCommand.RecoveringBlock;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeStorage;
@@ -58,7 +60,6 @@ import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
 import org.apache.hadoop.hdfs.server.protocol.ReplicaRecoveryInfo;
 import org.apache.hadoop.hdfs.server.protocol.StorageReport;
 import org.apache.hadoop.hdfs.server.protocol.VolumeFailureSummary;
-import org.apache.hadoop.util.DiskChecker.DiskErrorException;
 import org.apache.hadoop.util.ReflectionUtils;
 
 /**
@@ -92,8 +93,96 @@ public interface FsDatasetSpi<V extends FsVolumeSpi> extends FSDatasetMBean {
     }
   }
 
-  /** @return a list of volumes. */
-  public List<V> getVolumes();
+  /**
+   * It behaviors as an unmodifiable list of FsVolume. Individual FsVolume can
+   * be obtained by using {@link #get(int)}.
+   *
+   * This also holds the reference counts for these volumes. It releases all the
+   * reference counts in {@link #close()}.
+   */
+  class FsVolumeReferences implements Iterable<FsVolumeSpi>, Closeable {
+    private final List<FsVolumeReference> references;
+
+    public <S extends FsVolumeSpi> FsVolumeReferences(List<S> curVolumes) {
+      references = new ArrayList<>();
+      for (FsVolumeSpi v : curVolumes) {
+        try {
+          references.add(v.obtainReference());
+        } catch (ClosedChannelException e) {
+          // This volume has been closed.
+        }
+      }
+    }
+
+    private static class FsVolumeSpiIterator implements
+        Iterator<FsVolumeSpi> {
+      private final List<FsVolumeReference> references;
+      private int idx = 0;
+
+      FsVolumeSpiIterator(List<FsVolumeReference> refs) {
+        references = refs;
+      }
+
+      @Override
+      public boolean hasNext() {
+        return idx < references.size();
+      }
+
+      @Override
+      public FsVolumeSpi next() {
+        int refIdx = idx++;
+        return references.get(refIdx).getVolume();
+      }
+
+      @Override
+      public void remove() {
+        throw new UnsupportedOperationException();
+      }
+    }
+
+    @Override
+    public Iterator<FsVolumeSpi> iterator() {
+      return new FsVolumeSpiIterator(references);
+    }
+
+    /**
+     * Get the number of volumes.
+     */
+    public int size() {
+      return references.size();
+    }
+
+    /**
+     * Get the volume for a given index.
+     */
+    public FsVolumeSpi get(int index) {
+      return references.get(index).getVolume();
+    }
+
+    @Override
+    public void close() throws IOException {
+      IOException ioe = null;
+      for (FsVolumeReference ref : references) {
+        try {
+          ref.close();
+        } catch (IOException e) {
+          ioe = e;
+        }
+      }
+      references.clear();
+      if (ioe != null) {
+        throw ioe;
+      }
+    }
+  }
+
+  /**
+   * Returns a list of FsVolumes that hold reference counts.
+   *
+   * The caller must release the reference of each volume by calling
+   * {@link FsVolumeReferences#close()}.
+   */
+  public FsVolumeReferences getFsVolumeReferences();
 
   /**
    * Add a new volume to the FsDataset.<p/>

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsVolumeReference.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsVolumeReference.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsVolumeReference.java
index e61a059..8d39719 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsVolumeReference.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsVolumeReference.java
@@ -21,7 +21,7 @@ import java.io.Closeable;
 import java.io.IOException;
 
 /**
- * This is the interface for holding reference count as AutoClosable resource.
+ * This holds volume reference count as AutoClosable resource.
  * It increases the reference count by one in the constructor, and decreases
  * the reference count by one in {@link #close()}.
  *
@@ -37,12 +37,15 @@ import java.io.IOException;
  */
 public interface FsVolumeReference extends Closeable {
   /**
-   * Descrese the reference count of the volume.
+   * Decrease the reference count of the volume.
    * @throws IOException it never throws IOException.
    */
   @Override
-  public void close() throws IOException;
+  void close() throws IOException;
 
-  /** Returns the underlying volume object */
-  public FsVolumeSpi getVolume();
+  /**
+   * Returns the underlying volume object. Return null if the reference was
+   * released.
+   */
+  FsVolumeSpi getVolume();
 }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
index d72b8bf..31ac414 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
@@ -138,8 +138,8 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
   }
 
   @Override // FsDatasetSpi
-  public List<FsVolumeImpl> getVolumes() {
-    return volumes.getVolumes();
+  public FsVolumeReferences getFsVolumeReferences() {
+    return new FsVolumeReferences(volumes.getVolumes());
   }
 
   @Override
@@ -152,7 +152,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
       throws IOException {
     List<StorageReport> reports;
     synchronized (statsLock) {
-      List<FsVolumeImpl> curVolumes = getVolumes();
+      List<FsVolumeImpl> curVolumes = volumes.getVolumes();
       reports = new ArrayList<>(curVolumes.size());
       for (FsVolumeImpl volume : curVolumes) {
         try (FsVolumeReference ref = volume.obtainReference()) {
@@ -231,7 +231,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
     
   final DataNode datanode;
   final DataStorage dataStorage;
-  final FsVolumeList volumes;
+  private final FsVolumeList volumes;
   final Map<String, DatanodeStorage> storageMap;
   final FsDatasetAsyncDiskService asyncDiskService;
   final Daemon lazyWriter;
@@ -540,7 +540,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
    */
   @Override // FsDatasetSpi
   public boolean hasEnoughResource() {
-    return getVolumes().size() >= validVolsRequired; 
+    return volumes.getVolumes().size() >= validVolsRequired;
   }
 
   /**
@@ -1628,7 +1628,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
     Map<String, BlockListAsLongs.Builder> builders =
         new HashMap<String, BlockListAsLongs.Builder>();
 
-    List<FsVolumeImpl> curVolumes = getVolumes();
+    List<FsVolumeImpl> curVolumes = volumes.getVolumes();
     for (FsVolumeSpi v : curVolumes) {
       builders.put(v.getStorageID(), BlockListAsLongs.builder());
     }
@@ -2535,7 +2535,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
 
   private Collection<VolumeInfo> getVolumeInfo() {
     Collection<VolumeInfo> info = new ArrayList<VolumeInfo>();
-    for (FsVolumeImpl volume : getVolumes()) {
+    for (FsVolumeImpl volume : volumes.getVolumes()) {
       long used = 0;
       long free = 0;
       try (FsVolumeReference ref = volume.obtainReference()) {
@@ -2571,7 +2571,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
   @Override //FsDatasetSpi
   public synchronized void deleteBlockPool(String bpid, boolean force)
       throws IOException {
-    List<FsVolumeImpl> curVolumes = getVolumes();
+    List<FsVolumeImpl> curVolumes = volumes.getVolumes();
     if (!force) {
       for (FsVolumeImpl volume : curVolumes) {
         try (FsVolumeReference ref = volume.obtainReference()) {
@@ -2622,7 +2622,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
   @Override // FsDatasetSpi
   public HdfsBlocksMetadata getHdfsBlocksMetadata(String poolId,
       long[] blockIds) throws IOException {
-    List<FsVolumeImpl> curVolumes = getVolumes();
+    List<FsVolumeImpl> curVolumes = volumes.getVolumes();
     // List of VolumeIds, one per volume on the datanode
     List<byte[]> blocksVolumeIds = new ArrayList<>(curVolumes.size());
     // List of indexes into the list of VolumeIds, pointing at the VolumeId of
@@ -2730,7 +2730,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
   }
 
   private boolean ramDiskConfigured() {
-    for (FsVolumeImpl v: getVolumes()){
+    for (FsVolumeImpl v: volumes.getVolumes()){
       if (v.isTransientStorage()) {
         return true;
       }
@@ -2742,7 +2742,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
   // added or removed.
   // This should only be called when the FsDataSetImpl#volumes list is finalized.
   private void setupAsyncLazyPersistThreads() {
-    for (FsVolumeImpl v: getVolumes()){
+    for (FsVolumeImpl v: volumes.getVolumes()){
       setupAsyncLazyPersistThread(v);
     }
   }
@@ -2880,14 +2880,13 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
 
       // Don't worry about fragmentation for now. We don't expect more than one
       // transient volume per DN.
-      for (FsVolumeImpl v : getVolumes()) {
-        try (FsVolumeReference ref = v.obtainReference()) {
+      try (FsVolumeReferences volumes = getFsVolumeReferences()) {
+        for (FsVolumeSpi fvs : volumes) {
+          FsVolumeImpl v = (FsVolumeImpl) fvs;
           if (v.isTransientStorage()) {
             capacity += v.getCapacity();
             free += v.getAvailable();
           }
-        } catch (ClosedChannelException e) {
-          // ignore.
         }
       }
 

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
index 922ede5..bc96a02 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
@@ -198,7 +198,7 @@ public class FsVolumeImpl implements FsVolumeSpi {
   }
 
   private static class FsVolumeReferenceImpl implements FsVolumeReference {
-    private final FsVolumeImpl volume;
+    private FsVolumeImpl volume;
 
     FsVolumeReferenceImpl(FsVolumeImpl volume) throws ClosedChannelException {
       this.volume = volume;
@@ -211,7 +211,10 @@ public class FsVolumeImpl implements FsVolumeSpi {
      */
     @Override
     public void close() throws IOException {
-      volume.unreference();
+      if (volume != null) {
+        volume.unreference();
+        volume = null;
+      }
     }
 
     @Override

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
index d87595c..a73e129 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
@@ -276,10 +276,11 @@ class FsVolumeList {
    * @param ref       a reference to the new FsVolumeImpl instance.
    */
   void addVolume(FsVolumeReference ref) {
+    FsVolumeImpl volume = (FsVolumeImpl) ref.getVolume();
     while (true) {
       final FsVolumeImpl[] curVolumes = volumes.get();
       final List<FsVolumeImpl> volumeList = Lists.newArrayList(curVolumes);
-      volumeList.add((FsVolumeImpl)ref.getVolume());
+      volumeList.add(volume);
       if (volumes.compareAndSet(curVolumes,
           volumeList.toArray(new FsVolumeImpl[volumeList.size()]))) {
         break;
@@ -300,9 +301,9 @@ class FsVolumeList {
     }
     // If the volume is used to replace a failed volume, it needs to reset the
     // volume failure info for this volume.
-    removeVolumeFailureInfo(new File(ref.getVolume().getBasePath()));
+    removeVolumeFailureInfo(new File(volume.getBasePath()));
     FsDatasetImpl.LOG.info("Added new volume: " +
-        ref.getVolume().getStorageID());
+        volume.getStorageID());
   }
 
   /**

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java
index 8658e47..8aeaef8 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java
@@ -1493,15 +1493,20 @@ public class MiniDFSCluster {
     if (storageCapacities != null) {
       for (int i = curDatanodesNum; i < curDatanodesNum+numDataNodes; ++i) {
         final int index = i - curDatanodesNum;
-        List<? extends FsVolumeSpi> volumes = dns[index].getFSDataset().getVolumes();
-        assert storageCapacities[index].length == storagesPerDatanode;
-        assert volumes.size() == storagesPerDatanode;
-
-        for (int j = 0; j < volumes.size(); ++j) {
-          FsVolumeImpl volume = (FsVolumeImpl) volumes.get(j);
-          LOG.info("setCapacityForTesting "  + storageCapacities[index][j]
-              + " for [" + volume.getStorageType() + "]" + volume.getStorageID());
-          volume.setCapacityForTesting(storageCapacities[index][j]);
+        try (FsDatasetSpi.FsVolumeReferences volumes =
+            dns[index].getFSDataset().getFsVolumeReferences()) {
+          assert storageCapacities[index].length == storagesPerDatanode;
+          assert volumes.size() == storagesPerDatanode;
+
+          int j = 0;
+          for (FsVolumeSpi fvs : volumes) {
+            FsVolumeImpl volume = (FsVolumeImpl) fvs;
+            LOG.info("setCapacityForTesting " + storageCapacities[index][j]
+                + " for [" + volume.getStorageType() + "]" + volume
+                .getStorageID());
+            volume.setCapacityForTesting(storageCapacities[index][j]);
+            j++;
+          }
         }
       }
     }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSClusterWithNodeGroup.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSClusterWithNodeGroup.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSClusterWithNodeGroup.java
index ca2d8d6..b9682a1 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSClusterWithNodeGroup.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSClusterWithNodeGroup.java
@@ -20,7 +20,6 @@ package org.apache.hadoop.hdfs;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_DATANODE_HOST_NAME_KEY;
 
 import java.io.IOException;
-import java.util.List;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -31,7 +30,7 @@ import org.apache.hadoop.hdfs.server.datanode.DataNode;
 import org.apache.hadoop.hdfs.server.datanode.SecureDataNodeStarter;
 import org.apache.hadoop.hdfs.server.datanode.SimulatedFSDataset;
 import org.apache.hadoop.hdfs.server.datanode.SecureDataNodeStarter.SecureResources;
-import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl;
 import org.apache.hadoop.net.NetUtils;
 import org.apache.hadoop.net.StaticMapping;
@@ -195,12 +194,14 @@ public class MiniDFSClusterWithNodeGroup extends MiniDFSCluster {
 
     if (storageCapacities != null) {
       for (int i = curDatanodesNum; i < curDatanodesNum+numDataNodes; ++i) {
-        List<? extends FsVolumeSpi> volumes = dns[i].getFSDataset().getVolumes();
-        assert volumes.size() == storagesPerDatanode;
-
-        for (int j = 0; j < volumes.size(); ++j) {
-          FsVolumeImpl volume = (FsVolumeImpl) volumes.get(j);
-          volume.setCapacityForTesting(storageCapacities[i][j]);
+        try (FsDatasetSpi.FsVolumeReferences volumes =
+            dns[i].getFSDataset().getFsVolumeReferences()) {
+          assert volumes.size() == storagesPerDatanode;
+
+          for (int j = 0; j < volumes.size(); ++j) {
+            FsVolumeImpl volume = (FsVolumeImpl) volumes.get(j);
+            volume.setCapacityForTesting(storageCapacities[i][j]);
+          }
         }
       }
     }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestNameNodePrunesMissingStorages.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestNameNodePrunesMissingStorages.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestNameNodePrunesMissingStorages.java
index 4b97d01..78c1d27 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestNameNodePrunesMissingStorages.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestNameNodePrunesMissingStorages.java
@@ -33,6 +33,7 @@ import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
 import org.apache.hadoop.hdfs.server.datanode.DataNode;
 import org.apache.hadoop.hdfs.server.datanode.DataNodeTestUtils;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
 import org.apache.hadoop.hdfs.server.protocol.StorageReport;
@@ -43,9 +44,7 @@ import org.junit.Test;
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
-import java.util.Arrays;
 import java.util.Iterator;
-import java.util.List;
 
 import static org.hamcrest.core.Is.is;
 import static org.junit.Assert.assertThat;
@@ -199,15 +198,16 @@ public class TestNameNodePrunesMissingStorages {
         datanodeToRemoveStorageFromIdx++;
       }
       // Find the volume within the datanode which holds that first storage.
-      List<? extends FsVolumeSpi> volumes =
-          datanodeToRemoveStorageFrom.getFSDataset().getVolumes();
-      assertEquals(NUM_STORAGES_PER_DN, volumes.size());
       String volumeDirectoryToRemove = null;
-      for (FsVolumeSpi volume : volumes) {
-        if (volume.getStorageID().equals(storageIdToRemove)) {
-          volumeDirectoryToRemove = volume.getBasePath();
+      try (FsDatasetSpi.FsVolumeReferences volumes =
+          datanodeToRemoveStorageFrom.getFSDataset().getFsVolumeReferences()) {
+        assertEquals(NUM_STORAGES_PER_DN, volumes.size());
+        for (FsVolumeSpi volume : volumes) {
+          if (volume.getStorageID().equals(storageIdToRemove)) {
+            volumeDirectoryToRemove = volume.getBasePath();
+          }
         }
-      }
+      };
       // Shut down the datanode and remove the volume.
       // Replace the volume directory with a regular file, which will
       // cause a volume failure.  (If we merely removed the directory,

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/SimulatedFSDataset.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/SimulatedFSDataset.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/SimulatedFSDataset.java
index bc24237..2ac9416 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/SimulatedFSDataset.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/SimulatedFSDataset.java
@@ -1270,7 +1270,7 @@ public class SimulatedFSDataset implements FsDatasetSpi<FsVolumeSpi> {
   }
 
   @Override
-  public List<FsVolumeSpi> getVolumes() {
+  public FsVolumeReferences getFsVolumeReferences() {
     throw new UnsupportedOperationException();
   }
 

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockHasMultipleReplicasOnSameDN.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockHasMultipleReplicasOnSameDN.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockHasMultipleReplicasOnSameDN.java
index c47209e..c65ef85 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockHasMultipleReplicasOnSameDN.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockHasMultipleReplicasOnSameDN.java
@@ -27,8 +27,8 @@ import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hdfs.*;
 import org.apache.hadoop.hdfs.protocol.*;
-import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.hdfs.server.protocol.BlockReportContext;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeStorage;
 import org.apache.hadoop.hdfs.server.protocol.StorageBlockReport;
@@ -115,11 +115,13 @@ public class TestBlockHasMultipleReplicasOnSameDN {
       blocks.add(new FinalizedReplica(localBlock, null, null));
     }
 
-    BlockListAsLongs bll = BlockListAsLongs.encode(blocks);
-    for (int i = 0; i < cluster.getStoragesPerDatanode(); ++i) {
-      FsVolumeSpi v = dn.getFSDataset().getVolumes().get(i);
-      DatanodeStorage dns = new DatanodeStorage(v.getStorageID());
-      reports[i] = new StorageBlockReport(dns, bll);
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+      dn.getFSDataset().getFsVolumeReferences()) {
+      BlockListAsLongs bll = BlockListAsLongs.encode(blocks);
+      for (int i = 0; i < cluster.getStoragesPerDatanode(); ++i) {
+        DatanodeStorage dns = new DatanodeStorage(volumes.get(i).getStorageID());
+        reports[i] = new StorageBlockReport(dns, bll);
+      }
     }
 
     // Should not assert!

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockScanner.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockScanner.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockScanner.java
index 14e29e4..b01597a 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockScanner.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockScanner.java
@@ -82,7 +82,7 @@ public class TestBlockScanner {
     final DataNode datanode;
     final BlockScanner blockScanner;
     final FsDatasetSpi<? extends FsVolumeSpi> data;
-    final List<? extends FsVolumeSpi> volumes;
+    final FsDatasetSpi.FsVolumeReferences volumes;
 
     TestContext(Configuration conf, int numNameServices) throws Exception {
       this.numNameServices = numNameServices;
@@ -109,11 +109,12 @@ public class TestBlockScanner {
         dfs[i].mkdirs(new Path("/test"));
       }
       data = datanode.getFSDataset();
-      volumes = data.getVolumes();
+      volumes = data.getFsVolumeReferences();
     }
 
     @Override
     public void close() throws IOException {
+      volumes.close();
       if (cluster != null) {
         for (int i = 0; i < numNameServices; i++) {
           dfs[i].delete(new Path("/test"), true);
@@ -713,8 +714,7 @@ public class TestBlockScanner {
     ctx.createFiles(0, NUM_EXPECTED_BLOCKS, 1);
     final TestScanResultHandler.Info info =
         TestScanResultHandler.getInfo(ctx.volumes.get(0));
-    String storageID = ctx.datanode.getFSDataset().
-        getVolumes().get(0).getStorageID();
+    String storageID = ctx.volumes.get(0).getStorageID();
     synchronized (info) {
       info.sem = new Semaphore(4);
       info.shouldRun = true;

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeHotSwapVolumes.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeHotSwapVolumes.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeHotSwapVolumes.java
index 315529c..a396b0e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeHotSwapVolumes.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeHotSwapVolumes.java
@@ -517,9 +517,12 @@ public class TestDataNodeHotSwapVolumes {
 
     // Make sure that vol0 and vol2's metadata are not left in memory.
     FsDatasetSpi<?> dataset = dn.getFSDataset();
-    for (FsVolumeSpi volume : dataset.getVolumes()) {
-      assertThat(volume.getBasePath(), is(not(anyOf(
-          is(newDirs.get(0)), is(newDirs.get(2))))));
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+        dataset.getFsVolumeReferences()) {
+      for (FsVolumeSpi volume : volumes) {
+        assertThat(volume.getBasePath(), is(not(anyOf(
+            is(newDirs.get(0)), is(newDirs.get(2))))));
+      }
     }
     DataStorage storage = dn.getStorage();
     for (int i = 0; i < storage.getNumStorageDirs(); i++) {
@@ -688,10 +691,14 @@ public class TestDataNodeHotSwapVolumes {
   }
 
   /** Get the FsVolume on the given basePath */
-  private FsVolumeImpl getVolume(DataNode dn, File basePath) {
-    for (FsVolumeSpi vol : dn.getFSDataset().getVolumes()) {
-      if (vol.getBasePath().equals(basePath.getPath())) {
-        return (FsVolumeImpl)vol;
+  private FsVolumeImpl getVolume(DataNode dn, File basePath)
+      throws IOException {
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+      dn.getFSDataset().getFsVolumeReferences()) {
+      for (FsVolumeSpi vol : volumes) {
+        if (vol.getBasePath().equals(basePath.getPath())) {
+          return (FsVolumeImpl) vol;
+        }
       }
     }
     return null;

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeVolumeFailure.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeVolumeFailure.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeVolumeFailure.java
index 0d158c9..d38892c 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeVolumeFailure.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeVolumeFailure.java
@@ -63,7 +63,6 @@ import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetTestUtil;
 import org.apache.hadoop.hdfs.server.namenode.FSNamesystem;
-import org.apache.hadoop.hdfs.server.protocol.BlockReportContext;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeStorage;
 import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocols;
@@ -249,9 +248,11 @@ public class TestDataNodeVolumeFailure {
 
     // 2. dn0Vol1 is removed from FsDataset
     FsDatasetSpi<? extends FsVolumeSpi> data = dn0.getFSDataset();
-    for (FsVolumeSpi volume : data.getVolumes()) {
-      assertNotEquals(new File(volume.getBasePath()).getAbsoluteFile(),
-          dn0Vol1.getAbsoluteFile());
+    try (FsDatasetSpi.FsVolumeReferences vols = data.getFsVolumeReferences()) {
+      for (FsVolumeSpi volume : vols) {
+        assertNotEquals(new File(volume.getBasePath()).getAbsoluteFile(),
+            dn0Vol1.getAbsoluteFile());
+      }
     }
 
     // 3. all blocks on dn0Vol1 have been removed.

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDirectoryScanner.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDirectoryScanner.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDirectoryScanner.java
index 150b5e4..b225e35 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDirectoryScanner.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDirectoryScanner.java
@@ -157,30 +157,37 @@ public class TestDirectoryScanner {
   private void duplicateBlock(long blockId) throws IOException {
     synchronized (fds) {
       ReplicaInfo b = FsDatasetTestUtil.fetchReplicaInfo(fds, bpid, blockId);
-      for (FsVolumeSpi v : fds.getVolumes()) {
-        if (v.getStorageID().equals(b.getVolume().getStorageID())) {
-          continue;
-        }
-
-        // Volume without a copy of the block. Make a copy now.
-        File sourceBlock = b.getBlockFile();
-        File sourceMeta = b.getMetaFile();
-        String sourceRoot = b.getVolume().getBasePath();
-        String destRoot = v.getBasePath();
-
-        String relativeBlockPath = new File(sourceRoot).toURI().relativize(sourceBlock.toURI()).getPath();
-        String relativeMetaPath = new File(sourceRoot).toURI().relativize(sourceMeta.toURI()).getPath();
-
-        File destBlock = new File(destRoot, relativeBlockPath);
-        File destMeta = new File(destRoot, relativeMetaPath);
-
-        destBlock.getParentFile().mkdirs();
-        FileUtils.copyFile(sourceBlock, destBlock);
-        FileUtils.copyFile(sourceMeta, destMeta);
+      try (FsDatasetSpi.FsVolumeReferences volumes =
+          fds.getFsVolumeReferences()) {
+        for (FsVolumeSpi v : volumes) {
+          if (v.getStorageID().equals(b.getVolume().getStorageID())) {
+            continue;
+          }
 
-        if (destBlock.exists() && destMeta.exists()) {
-          LOG.info("Copied " + sourceBlock + " ==> " + destBlock);
-          LOG.info("Copied " + sourceMeta + " ==> " + destMeta);
+          // Volume without a copy of the block. Make a copy now.
+          File sourceBlock = b.getBlockFile();
+          File sourceMeta = b.getMetaFile();
+          String sourceRoot = b.getVolume().getBasePath();
+          String destRoot = v.getBasePath();
+
+          String relativeBlockPath =
+              new File(sourceRoot).toURI().relativize(sourceBlock.toURI())
+                  .getPath();
+          String relativeMetaPath =
+              new File(sourceRoot).toURI().relativize(sourceMeta.toURI())
+                  .getPath();
+
+          File destBlock = new File(destRoot, relativeBlockPath);
+          File destMeta = new File(destRoot, relativeMetaPath);
+
+          destBlock.getParentFile().mkdirs();
+          FileUtils.copyFile(sourceBlock, destBlock);
+          FileUtils.copyFile(sourceMeta, destMeta);
+
+          if (destBlock.exists() && destMeta.exists()) {
+            LOG.info("Copied " + sourceBlock + " ==> " + destBlock);
+            LOG.info("Copied " + sourceMeta + " ==> " + destMeta);
+          }
         }
       }
     }
@@ -209,58 +216,67 @@ public class TestDirectoryScanner {
 
   /** Create a block file in a random volume*/
   private long createBlockFile() throws IOException {
-    List<? extends FsVolumeSpi> volumes = fds.getVolumes();
-    int index = rand.nextInt(volumes.size() - 1);
     long id = getFreeBlockId();
-    File finalizedDir = volumes.get(index).getFinalizedDir(bpid);
-    File file = new File(finalizedDir, getBlockFile(id));
-    if (file.createNewFile()) {
-      LOG.info("Created block file " + file.getName());
+    try (FsDatasetSpi.FsVolumeReferences volumes = fds.getFsVolumeReferences()) {
+      int numVolumes = volumes.size();
+      int index = rand.nextInt(numVolumes - 1);
+      File finalizedDir = volumes.get(index).getFinalizedDir(bpid);
+      File file = new File(finalizedDir, getBlockFile(id));
+      if (file.createNewFile()) {
+        LOG.info("Created block file " + file.getName());
+      }
     }
     return id;
   }
 
   /** Create a metafile in a random volume*/
   private long createMetaFile() throws IOException {
-    List<? extends FsVolumeSpi> volumes = fds.getVolumes();
-    int index = rand.nextInt(volumes.size() - 1);
     long id = getFreeBlockId();
-    File finalizedDir = volumes.get(index).getFinalizedDir(bpid);
-    File file = new File(finalizedDir, getMetaFile(id));
-    if (file.createNewFile()) {
-      LOG.info("Created metafile " + file.getName());
+    try (FsDatasetSpi.FsVolumeReferences refs = fds.getFsVolumeReferences()) {
+      int numVolumes = refs.size();
+      int index = rand.nextInt(numVolumes - 1);
+
+      File finalizedDir = refs.get(index).getFinalizedDir(bpid);
+      File file = new File(finalizedDir, getMetaFile(id));
+      if (file.createNewFile()) {
+        LOG.info("Created metafile " + file.getName());
+      }
     }
     return id;
   }
 
   /** Create block file and corresponding metafile in a rondom volume */
   private long createBlockMetaFile() throws IOException {
-    List<? extends FsVolumeSpi> volumes = fds.getVolumes();
-    int index = rand.nextInt(volumes.size() - 1);
     long id = getFreeBlockId();
-    File finalizedDir = volumes.get(index).getFinalizedDir(bpid);
-    File file = new File(finalizedDir, getBlockFile(id));
-    if (file.createNewFile()) {
-      LOG.info("Created block file " + file.getName());
-
-      // Create files with same prefix as block file but extension names
-      // such that during sorting, these files appear around meta file
-      // to test how DirectoryScanner handles extraneous files
-      String name1 = file.getAbsolutePath() + ".l";
-      String name2 = file.getAbsolutePath() + ".n";
-      file = new File(name1);
-      if (file.createNewFile()) {
-        LOG.info("Created extraneous file " + name1);
-      }
 
-      file = new File(name2);
-      if (file.createNewFile()) {
-        LOG.info("Created extraneous file " + name2);
-      }
+    try (FsDatasetSpi.FsVolumeReferences refs = fds.getFsVolumeReferences()) {
+      int numVolumes = refs.size();
+      int index = rand.nextInt(numVolumes - 1);
 
-      file = new File(finalizedDir, getMetaFile(id));
+      File finalizedDir = refs.get(index).getFinalizedDir(bpid);
+      File file = new File(finalizedDir, getBlockFile(id));
       if (file.createNewFile()) {
-        LOG.info("Created metafile " + file.getName());
+        LOG.info("Created block file " + file.getName());
+
+        // Create files with same prefix as block file but extension names
+        // such that during sorting, these files appear around meta file
+        // to test how DirectoryScanner handles extraneous files
+        String name1 = file.getAbsolutePath() + ".l";
+        String name2 = file.getAbsolutePath() + ".n";
+        file = new File(name1);
+        if (file.createNewFile()) {
+          LOG.info("Created extraneous file " + name1);
+        }
+
+        file = new File(name2);
+        if (file.createNewFile()) {
+          LOG.info("Created extraneous file " + name2);
+        }
+
+        file = new File(finalizedDir, getMetaFile(id));
+        if (file.createNewFile()) {
+          LOG.info("Created metafile " + file.getName());
+        }
       }
     }
     return id;

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDiskError.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDiskError.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDiskError.java
index 3ec76db..cc8566c 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDiskError.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDiskError.java
@@ -42,6 +42,7 @@ import org.apache.hadoop.hdfs.protocol.LocatedBlocks;
 import org.apache.hadoop.hdfs.protocol.datatransfer.BlockConstructionStage;
 import org.apache.hadoop.hdfs.protocol.datatransfer.Sender;
 import org.apache.hadoop.hdfs.security.token.block.BlockTokenSecretManager;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.hdfs.server.namenode.NameNodeAdapter;
 import org.apache.hadoop.util.DataChecksum;
@@ -190,12 +191,15 @@ public class TestDiskError {
     // Check permissions on directories in 'dfs.datanode.data.dir'
     FileSystem localFS = FileSystem.getLocal(conf);
     for (DataNode dn : cluster.getDataNodes()) {
-      for (FsVolumeSpi v : dn.getFSDataset().getVolumes()) {
-        String dir = v.getBasePath();
-        Path dataDir = new Path(dir);
-        FsPermission actual = localFS.getFileStatus(dataDir).getPermission();
+      try (FsDatasetSpi.FsVolumeReferences volumes =
+          dn.getFSDataset().getFsVolumeReferences()) {
+        for (FsVolumeSpi vol : volumes) {
+          String dir = vol.getBasePath();
+          Path dataDir = new Path(dir);
+          FsPermission actual = localFS.getFileStatus(dataDir).getPermission();
           assertEquals("Permission for dir: " + dataDir + ", is " + actual +
               ", while expected is " + expected, expected, actual);
+        }
       }
     }
   }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBlockReports.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBlockReports.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBlockReports.java
index f27a78e..de73dcf 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBlockReports.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBlockReports.java
@@ -31,6 +31,7 @@ import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.*;
 import org.apache.hadoop.hdfs.protocol.Block;
 import org.apache.hadoop.hdfs.protocolPB.DatanodeProtocolClientSideTranslatorPB;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
 import org.apache.hadoop.hdfs.server.protocol.ReceivedDeletedBlockInfo;
@@ -71,7 +72,10 @@ public class TestIncrementalBlockReports {
     singletonDn = cluster.getDataNodes().get(0);
     bpos = singletonDn.getAllBpOs().get(0);
     actor = bpos.getBPServiceActors().get(0);
-    storageUuid = singletonDn.getFSDataset().getVolumes().get(0).getStorageID();
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+        singletonDn.getFSDataset().getFsVolumeReferences()) {
+      storageUuid = volumes.get(0).getStorageID();
+    }
   }
 
   private static Block getDummyBlock() {

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBrVariations.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBrVariations.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBrVariations.java
index 4e73e6e..989e216 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBrVariations.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestIncrementalBrVariations.java
@@ -29,7 +29,6 @@ import java.util.UUID;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-import org.apache.commons.logging.impl.Log4JLogger;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hdfs.DFSClient;
@@ -39,6 +38,7 @@ import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.hdfs.protocol.*;
 import org.apache.hadoop.hdfs.server.blockmanagement.BlockManager;
 import org.apache.hadoop.hdfs.server.blockmanagement.DatanodeStorageInfo;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.hdfs.server.namenode.FSNamesystem;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
@@ -142,48 +142,55 @@ public class TestIncrementalBrVariations {
     // Get the block list for the file with the block locations.
     LocatedBlocks blocks = createFileGetBlocks(GenericTestUtils.getMethodName());
 
-    // We will send 'fake' incremental block reports to the NN that look
-    // like they originated from DN 0.
-    StorageReceivedDeletedBlocks reports[] =
-        new StorageReceivedDeletedBlocks[dn0.getFSDataset().getVolumes().size()];
-
-    // Lie to the NN that one block on each storage has been deleted.
-    for (int i = 0; i < reports.length; ++i) {
-      FsVolumeSpi volume = dn0.getFSDataset().getVolumes().get(i);
-
-      boolean foundBlockOnStorage = false;
-      ReceivedDeletedBlockInfo rdbi[] = new ReceivedDeletedBlockInfo[1];
-
-      // Find the first block on this storage and mark it as deleted for the
-      // report.
-      for (LocatedBlock block : blocks.getLocatedBlocks()) {
-        if (block.getStorageIDs()[0].equals(volume.getStorageID())) {
-          rdbi[0] = new ReceivedDeletedBlockInfo(block.getBlock().getLocalBlock(),
-              ReceivedDeletedBlockInfo.BlockStatus.DELETED_BLOCK, null);
-          foundBlockOnStorage = true;
-          break;
+    try (FsDatasetSpi.FsVolumeReferences volumes
+        = dn0.getFSDataset().getFsVolumeReferences()) {
+      // We will send 'fake' incremental block reports to the NN that look
+      // like they originated from DN 0.
+      StorageReceivedDeletedBlocks reports[] =
+          new StorageReceivedDeletedBlocks[volumes.size()];
+
+      // Lie to the NN that one block on each storage has been deleted.
+      for (int i = 0; i < reports.length; ++i) {
+        FsVolumeSpi volume = volumes.get(i);
+
+        boolean foundBlockOnStorage = false;
+        ReceivedDeletedBlockInfo rdbi[] = new ReceivedDeletedBlockInfo[1];
+
+        // Find the first block on this storage and mark it as deleted for the
+        // report.
+        for (LocatedBlock block : blocks.getLocatedBlocks()) {
+          if (block.getStorageIDs()[0].equals(volume.getStorageID())) {
+            rdbi[0] =
+                new ReceivedDeletedBlockInfo(block.getBlock().getLocalBlock(),
+                    ReceivedDeletedBlockInfo.BlockStatus.DELETED_BLOCK, null);
+            foundBlockOnStorage = true;
+            break;
+          }
         }
-      }
 
-      assertTrue(foundBlockOnStorage);
-      reports[i] = new StorageReceivedDeletedBlocks(volume.getStorageID(), rdbi);
+        assertTrue(foundBlockOnStorage);
+        reports[i] =
+            new StorageReceivedDeletedBlocks(volume.getStorageID(), rdbi);
 
-      if (splitReports) {
-        // If we are splitting reports then send the report for this storage now.
-        StorageReceivedDeletedBlocks singletonReport[] = { reports[i] };
-        cluster.getNameNodeRpc().blockReceivedAndDeleted(
-            dn0Reg, poolId, singletonReport);
+        if (splitReports) {
+          // If we are splitting reports then send the report for this storage now.
+          StorageReceivedDeletedBlocks singletonReport[] = { reports[i] };
+          cluster.getNameNodeRpc().blockReceivedAndDeleted(
+              dn0Reg, poolId, singletonReport);
+        }
       }
-    }
 
-    if (!splitReports) {
-      // Send a combined report.
-      cluster.getNameNodeRpc().blockReceivedAndDeleted(dn0Reg, poolId, reports);
-    }
+      if (!splitReports) {
+        // Send a combined report.
+        cluster.getNameNodeRpc()
+            .blockReceivedAndDeleted(dn0Reg, poolId, reports);
+      }
 
-    // Make sure that the deleted block from each storage was picked up
-    // by the NameNode.
-    assertThat(cluster.getNamesystem().getMissingBlocksCount(), is((long) reports.length));
+      // Make sure that the deleted block from each storage was picked up
+      // by the NameNode.
+      assertThat(cluster.getNamesystem().getMissingBlocksCount(),
+          is((long) reports.length));
+    }
   }
 
   /**

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestTriggerBlockReport.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestTriggerBlockReport.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestTriggerBlockReport.java
index c2348e3..00c0f22 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestTriggerBlockReport.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestTriggerBlockReport.java
@@ -33,6 +33,7 @@ import org.apache.hadoop.hdfs.client.BlockReportOptions;
 import org.apache.hadoop.hdfs.protocol.Block;
 import org.apache.hadoop.hdfs.protocolPB.DatanodeProtocolClientSideTranslatorPB;
 import org.apache.hadoop.hdfs.server.protocol.BlockReportContext;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
 import org.apache.hadoop.hdfs.server.protocol.ReceivedDeletedBlockInfo;
 import org.apache.hadoop.hdfs.server.protocol.ReceivedDeletedBlockInfo.BlockStatus;
@@ -92,8 +93,11 @@ public final class TestTriggerBlockReport {
     DataNode datanode = cluster.getDataNodes().get(0);
     BPServiceActor actor =
         datanode.getAllBpOs().get(0).getBPServiceActors().get(0);
-    String storageUuid =
-        datanode.getFSDataset().getVolumes().get(0).getStorageID();
+    String storageUuid;
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+        datanode.getFSDataset().getFsVolumeReferences()) {
+      storageUuid = volumes.get(0).getStorageID();
+    }
     actor.notifyNamenodeDeletedBlock(rdbi, storageUuid);
 
     // Manually trigger a block report.

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java
index b7c2028..28666a0 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java
@@ -51,7 +51,7 @@ public class ExternalDatasetImpl implements FsDatasetSpi<ExternalVolumeImpl> {
       StorageType.DEFAULT);
 
   @Override
-  public List<ExternalVolumeImpl> getVolumes() {
+  public FsVolumeReferences getFsVolumeReferences() {
     return null;
   }
 

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/LazyPersistTestCase.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/LazyPersistTestCase.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/LazyPersistTestCase.java
index 7e1aa81..5dc86f7 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/LazyPersistTestCase.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/LazyPersistTestCase.java
@@ -43,7 +43,6 @@ import java.io.IOException;
 import java.util.Arrays;
 import java.util.EnumSet;
 import java.util.HashSet;
-import java.util.List;
 import java.util.Set;
 import java.util.UUID;
 
@@ -62,11 +61,11 @@ import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.DFSTestUtil;
 import org.apache.hadoop.hdfs.DistributedFileSystem;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
-import org.apache.hadoop.hdfs.client.HdfsClientConfigKeys;
 import org.apache.hadoop.hdfs.protocol.LocatedBlock;
 import org.apache.hadoop.hdfs.protocol.LocatedBlocks;
 import org.apache.hadoop.hdfs.server.datanode.DataNodeTestUtils;
 import org.apache.hadoop.hdfs.server.datanode.DatanodeUtil;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.hdfs.tools.JMXGet;
 import org.apache.hadoop.net.unix.TemporarySocketDirectory;
@@ -155,30 +154,34 @@ public abstract class LazyPersistTestCase {
   protected final void ensureLazyPersistBlocksAreSaved(
       LocatedBlocks locatedBlocks) throws IOException, InterruptedException {
     final String bpid = cluster.getNamesystem().getBlockPoolId();
-    List<? extends FsVolumeSpi> volumes =
-      cluster.getDataNodes().get(0).getFSDataset().getVolumes();
-    final Set<Long> persistedBlockIds = new HashSet<Long>();
 
-    while (persistedBlockIds.size() < locatedBlocks.getLocatedBlocks().size()) {
-      // Take 1 second sleep before each verification iteration
-      Thread.sleep(1000);
-
-      for (LocatedBlock lb : locatedBlocks.getLocatedBlocks()) {
-        for (FsVolumeSpi v : volumes) {
-          if (v.isTransientStorage()) {
-            continue;
-          }
-
-          FsVolumeImpl volume = (FsVolumeImpl) v;
-          File lazyPersistDir = volume.getBlockPoolSlice(bpid).getLazypersistDir();
+    final Set<Long> persistedBlockIds = new HashSet<Long>();
 
-          long blockId = lb.getBlock().getBlockId();
-          File targetDir =
-            DatanodeUtil.idToBlockDir(lazyPersistDir, blockId);
-          File blockFile = new File(targetDir, lb.getBlock().getBlockName());
-          if (blockFile.exists()) {
-            // Found a persisted copy for this block and added to the Set
-            persistedBlockIds.add(blockId);
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+        cluster.getDataNodes().get(0).getFSDataset().getFsVolumeReferences()) {
+      while (persistedBlockIds.size() < locatedBlocks.getLocatedBlocks()
+          .size()) {
+        // Take 1 second sleep before each verification iteration
+        Thread.sleep(1000);
+
+        for (LocatedBlock lb : locatedBlocks.getLocatedBlocks()) {
+          for (FsVolumeSpi v : volumes) {
+            if (v.isTransientStorage()) {
+              continue;
+            }
+
+            FsVolumeImpl volume = (FsVolumeImpl) v;
+            File lazyPersistDir =
+                volume.getBlockPoolSlice(bpid).getLazypersistDir();
+
+            long blockId = lb.getBlock().getBlockId();
+            File targetDir =
+                DatanodeUtil.idToBlockDir(lazyPersistDir, blockId);
+            File blockFile = new File(targetDir, lb.getBlock().getBlockName());
+            if (blockFile.exists()) {
+              // Found a persisted copy for this block and added to the Set
+              persistedBlockIds.add(blockId);
+            }
           }
         }
       }
@@ -432,18 +435,21 @@ public abstract class LazyPersistTestCase {
     }
 
     final String bpid = cluster.getNamesystem().getBlockPoolId();
-    List<? extends FsVolumeSpi> volumes =
-      cluster.getDataNodes().get(0).getFSDataset().getVolumes();
+    final FsDatasetSpi<?> dataset =
+        cluster.getDataNodes().get(0).getFSDataset();
 
     // Make sure deleted replica does not have a copy on either finalized dir of
     // transient volume or finalized dir of non-transient volume
-    for (FsVolumeSpi v : volumes) {
-      FsVolumeImpl volume = (FsVolumeImpl) v;
-      File targetDir = (v.isTransientStorage()) ?
-          volume.getBlockPoolSlice(bpid).getFinalizedDir() :
-          volume.getBlockPoolSlice(bpid).getLazypersistDir();
-      if (verifyBlockDeletedFromDir(targetDir, locatedBlocks) == false) {
-        return false;
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+        dataset.getFsVolumeReferences()) {
+      for (FsVolumeSpi vol : volumes) {
+        FsVolumeImpl volume = (FsVolumeImpl) vol;
+        File targetDir = (volume.isTransientStorage()) ?
+            volume.getBlockPoolSlice(bpid).getFinalizedDir() :
+            volume.getBlockPoolSlice(bpid).getLazypersistDir();
+        if (verifyBlockDeletedFromDir(targetDir, locatedBlocks) == false) {
+          return false;
+        }
       }
     }
     return true;

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestDatanodeRestart.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestDatanodeRestart.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestDatanodeRestart.java
index a91baec..a5a09fa 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestDatanodeRestart.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestDatanodeRestart.java
@@ -40,6 +40,7 @@ import org.apache.hadoop.hdfs.server.datanode.DataNode;
 import org.apache.hadoop.hdfs.server.datanode.DataNodeTestUtils;
 import org.apache.hadoop.hdfs.server.datanode.DatanodeUtil;
 import org.apache.hadoop.hdfs.server.datanode.ReplicaInfo;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.io.IOUtils;
 import org.junit.Assert;
@@ -101,13 +102,18 @@ public class TestDatanodeRestart {
       out.write(writeBuf);
       out.hflush();
       DataNode dn = cluster.getDataNodes().get(0);
-      for (FsVolumeSpi v : dataset(dn).getVolumes()) {
-        final FsVolumeImpl volume = (FsVolumeImpl)v;
-        File currentDir = volume.getCurrentDir().getParentFile().getParentFile();
-        File rbwDir = new File(currentDir, "rbw");
-        for (File file : rbwDir.listFiles()) {
-          if (isCorrupt && Block.isBlockFilename(file)) {
-            new RandomAccessFile(file, "rw").setLength(fileLen-1); // corrupt
+      try (FsDatasetSpi.FsVolumeReferences volumes =
+          dataset(dn).getFsVolumeReferences()) {
+        for (FsVolumeSpi vol : volumes) {
+          final FsVolumeImpl volume = (FsVolumeImpl) vol;
+          File currentDir =
+              volume.getCurrentDir().getParentFile().getParentFile();
+          File rbwDir = new File(currentDir, "rbw");
+          for (File file : rbwDir.listFiles()) {
+            if (isCorrupt && Block.isBlockFilename(file)) {
+              new RandomAccessFile(file, "rw")
+                  .setLength(fileLen - 1); // corrupt
+            }
           }
         }
       }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsDatasetImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsDatasetImpl.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsDatasetImpl.java
index 56a4287..9f4f700 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsDatasetImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsDatasetImpl.java
@@ -40,6 +40,7 @@ import org.apache.hadoop.hdfs.server.datanode.FinalizedReplica;
 import org.apache.hadoop.hdfs.server.datanode.ReplicaHandler;
 import org.apache.hadoop.hdfs.server.datanode.ReplicaInfo;
 import org.apache.hadoop.hdfs.server.datanode.StorageLocation;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeReference;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.RoundRobinVolumeChoosingPolicy;
 import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
@@ -56,7 +57,6 @@ import org.mockito.stubbing.Answer;
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
@@ -68,7 +68,6 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 import static org.mockito.Matchers.any;
-import static org.mockito.Matchers.anyList;
 import static org.mockito.Matchers.anyListOf;
 import static org.mockito.Matchers.anyString;
 import static org.mockito.Matchers.eq;
@@ -124,6 +123,15 @@ public class TestFsDatasetImpl {
     when(storage.getNumStorageDirs()).thenReturn(numDirs);
   }
 
+  private int getNumVolumes() {
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+        dataset.getFsVolumeReferences()) {
+      return volumes.size();
+    } catch (IOException e) {
+      return 0;
+    }
+  }
+
   @Before
   public void setUp() throws IOException {
     datanode = mock(DataNode.class);
@@ -143,14 +151,14 @@ public class TestFsDatasetImpl {
       dataset.addBlockPool(bpid, conf);
     }
 
-    assertEquals(NUM_INIT_VOLUMES, dataset.getVolumes().size());
+    assertEquals(NUM_INIT_VOLUMES, getNumVolumes());
     assertEquals(0, dataset.getNumFailedVolumes());
   }
 
   @Test
   public void testAddVolumes() throws IOException {
     final int numNewVolumes = 3;
-    final int numExistingVolumes = dataset.getVolumes().size();
+    final int numExistingVolumes = getNumVolumes();
     final int totalVolumes = numNewVolumes + numExistingVolumes;
     Set<String> expectedVolumes = new HashSet<String>();
     List<NamespaceInfo> nsInfos = Lists.newArrayList();
@@ -172,13 +180,15 @@ public class TestFsDatasetImpl {
       dataset.addVolume(loc, nsInfos);
     }
 
-    assertEquals(totalVolumes, dataset.getVolumes().size());
+    assertEquals(totalVolumes, getNumVolumes());
     assertEquals(totalVolumes, dataset.storageMap.size());
 
     Set<String> actualVolumes = new HashSet<String>();
-    for (int i = 0; i < numNewVolumes; i++) {
-      actualVolumes.add(
-          dataset.getVolumes().get(numExistingVolumes + i).getBasePath());
+    try (FsDatasetSpi.FsVolumeReferences volumes =
+        dataset.getFsVolumeReferences()) {
+      for (int i = 0; i < numNewVolumes; i++) {
+        actualVolumes.add(volumes.get(numExistingVolumes + i).getBasePath());
+      }
     }
     assertEquals(actualVolumes.size(), expectedVolumes.size());
     assertTrue(actualVolumes.containsAll(expectedVolumes));
@@ -204,7 +214,7 @@ public class TestFsDatasetImpl {
     dataset.removeVolumes(volumesToRemove, true);
     int expectedNumVolumes = dataDirs.length - 1;
     assertEquals("The volume has been removed from the volumeList.",
-        expectedNumVolumes, dataset.getVolumes().size());
+        expectedNumVolumes, getNumVolumes());
     assertEquals("The volume has been removed from the storageMap.",
         expectedNumVolumes, dataset.storageMap.size());
 
@@ -231,7 +241,7 @@ public class TestFsDatasetImpl {
 
   @Test(timeout = 5000)
   public void testRemoveNewlyAddedVolume() throws IOException {
-    final int numExistingVolumes = dataset.getVolumes().size();
+    final int numExistingVolumes = getNumVolumes();
     List<NamespaceInfo> nsInfos = new ArrayList<>();
     for (String bpid : BLOCK_POOL_IDS) {
       nsInfos.add(new NamespaceInfo(0, CLUSTER_ID, bpid, 1));
@@ -247,14 +257,14 @@ public class TestFsDatasetImpl {
         .thenReturn(builder);
 
     dataset.addVolume(loc, nsInfos);
-    assertEquals(numExistingVolumes + 1, dataset.getVolumes().size());
+    assertEquals(numExistingVolumes + 1, getNumVolumes());
 
     when(storage.getNumStorageDirs()).thenReturn(numExistingVolumes + 1);
     when(storage.getStorageDir(numExistingVolumes)).thenReturn(sd);
     Set<File> volumesToRemove = new HashSet<>();
     volumesToRemove.add(loc.getFile());
     dataset.removeVolumes(volumesToRemove, true);
-    assertEquals(numExistingVolumes, dataset.getVolumes().size());
+    assertEquals(numExistingVolumes, getNumVolumes());
   }
 
   @Test(timeout = 5000)
@@ -357,7 +367,10 @@ public class TestFsDatasetImpl {
       DataNode dn = cluster.getDataNodes().get(0);
       
       FsDatasetImpl ds = (FsDatasetImpl) DataNodeTestUtils.getFSDataset(dn);
-      FsVolumeImpl vol = ds.getVolumes().get(0);
+      FsVolumeImpl vol;
+      try (FsDatasetSpi.FsVolumeReferences volumes = ds.getFsVolumeReferences()) {
+        vol = (FsVolumeImpl)volumes.get(0);
+      }
 
       ExtendedBlock eb;
       ReplicaInfo info;

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsVolumeList.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsVolumeList.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsVolumeList.java
index eccff89..9b9b692 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsVolumeList.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsVolumeList.java
@@ -35,7 +35,7 @@ import java.util.Collections;
 import java.util.List;
 
 import static org.junit.Assert.assertNotEquals;
-import static org.junit.Assert.fail;
+import static org.junit.Assert.assertNull;
 import static org.mockito.Mockito.mock;
 
 public class TestFsVolumeList {
@@ -113,11 +113,6 @@ public class TestFsVolumeList {
         conf, StorageType.DEFAULT);
     FsVolumeReference ref = volume.obtainReference();
     volumeList.addVolume(ref);
-    try {
-      ref.close();
-      fail("Should throw exception because the reference is closed in "
-          + "VolumeList#addVolume().");
-    } catch (IllegalStateException e) {
-    }
+    assertNull(ref.getVolume());
   }
 }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestRbwSpaceReservation.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestRbwSpaceReservation.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestRbwSpaceReservation.java
index ebf2f3b..9b83b39 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestRbwSpaceReservation.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestRbwSpaceReservation.java
@@ -32,7 +32,8 @@ import org.apache.hadoop.fs.FSDataOutputStream;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hdfs.*;
 import org.apache.hadoop.hdfs.server.datanode.DataNode;
-import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeReference;
 import org.apache.hadoop.ipc.RemoteException;
 import org.apache.hadoop.test.GenericTestUtils;
 import org.apache.hadoop.util.Daemon;
@@ -44,7 +45,6 @@ import org.junit.rules.ExpectedException;
 
 import java.io.IOException;
 import java.io.OutputStream;
-import java.util.List;
 import java.util.Random;
 import java.util.concurrent.TimeoutException;
 
@@ -64,6 +64,7 @@ public class TestRbwSpaceReservation {
   private Configuration conf;
   private DistributedFileSystem fs = null;
   private DFSClient client = null;
+  FsVolumeReference singletonVolumeRef = null;
   FsVolumeImpl singletonVolume = null;
 
   private static Random rand = new Random();
@@ -104,23 +105,22 @@ public class TestRbwSpaceReservation {
     cluster.waitActive();
 
     if (perVolumeCapacity >= 0) {
-      for (DataNode dn : cluster.getDataNodes()) {
-        for (FsVolumeSpi volume : dn.getFSDataset().getVolumes()) {
-          ((FsVolumeImpl) volume).setCapacityForTesting(perVolumeCapacity);
-        }
+      try (FsDatasetSpi.FsVolumeReferences volumes =
+          cluster.getDataNodes().get(0).getFSDataset().getFsVolumeReferences()) {
+        singletonVolumeRef = volumes.get(0).obtainReference();
       }
-    }
-
-    if (numDatanodes == 1) {
-      List<? extends FsVolumeSpi> volumes =
-          cluster.getDataNodes().get(0).getFSDataset().getVolumes();
-      assertThat(volumes.size(), is(1));
-      singletonVolume = ((FsVolumeImpl) volumes.get(0));
+      singletonVolume = ((FsVolumeImpl) singletonVolumeRef.getVolume());
+      singletonVolume.setCapacityForTesting(perVolumeCapacity);
     }
   }
 
   @After
   public void shutdownCluster() throws IOException {
+    if (singletonVolumeRef != null) {
+      singletonVolumeRef.close();
+      singletonVolumeRef = null;
+    }
+
     if (client != null) {
       client.close();
       client = null;
@@ -266,13 +266,16 @@ public class TestRbwSpaceReservation {
     // Ensure all space reserved for the replica was released on each
     // DataNode.
     for (DataNode dn : cluster.getDataNodes()) {
-      final FsVolumeImpl volume = (FsVolumeImpl) dn.getFSDataset().getVolumes().get(0);
-      GenericTestUtils.waitFor(new Supplier<Boolean>() {
-        @Override
-        public Boolean get() {
-          return (volume.getReservedForRbw() == 0);
-        }
-      }, 500, Integer.MAX_VALUE); // Wait until the test times out.
+      try (FsDatasetSpi.FsVolumeReferences volumes =
+          dn.getFSDataset().getFsVolumeReferences()) {
+        final FsVolumeImpl volume = (FsVolumeImpl) volumes.get(0);
+        GenericTestUtils.waitFor(new Supplier<Boolean>() {
+          @Override
+          public Boolean get() {
+            return (volume.getReservedForRbw() == 0);
+          }
+        }, 500, Integer.MAX_VALUE); // Wait until the test times out.
+      }
     }
   }
 

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestWriteToReplica.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestWriteToReplica.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestWriteToReplica.java
index 96a73c6..d5664cf 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestWriteToReplica.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestWriteToReplica.java
@@ -45,6 +45,8 @@ import org.apache.hadoop.hdfs.server.datanode.ReplicaInfo;
 import org.apache.hadoop.hdfs.server.datanode.ReplicaNotFoundException;
 import org.apache.hadoop.hdfs.server.datanode.ReplicaUnderRecovery;
 import org.apache.hadoop.hdfs.server.datanode.ReplicaWaitingToBeRecovered;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
 import org.apache.hadoop.util.DiskChecker.DiskOutOfSpaceException;
 import org.junit.Assert;
@@ -161,31 +163,37 @@ public class TestWriteToReplica {
     };
     
     ReplicaMap replicasMap = dataSet.volumeMap;
-    FsVolumeImpl vol = (FsVolumeImpl) dataSet.volumes
-        .getNextVolume(StorageType.DEFAULT, 0).getVolume();
-    ReplicaInfo replicaInfo = new FinalizedReplica(
-        blocks[FINALIZED].getLocalBlock(), vol, vol.getCurrentDir().getParentFile());
-    replicasMap.add(bpid, replicaInfo);
-    replicaInfo.getBlockFile().createNewFile();
-    replicaInfo.getMetaFile().createNewFile();
-    
-    replicasMap.add(bpid, new ReplicaInPipeline(
-        blocks[TEMPORARY].getBlockId(),
-        blocks[TEMPORARY].getGenerationStamp(), vol,
-        vol.createTmpFile(bpid, blocks[TEMPORARY].getLocalBlock()).getParentFile(), 0));
-    
-    replicaInfo = new ReplicaBeingWritten(blocks[RBW].getLocalBlock(), vol,
-        vol.createRbwFile(bpid, blocks[RBW].getLocalBlock()).getParentFile(), null);
-    replicasMap.add(bpid, replicaInfo);
-    replicaInfo.getBlockFile().createNewFile();
-    replicaInfo.getMetaFile().createNewFile();
-    
-    replicasMap.add(bpid, new ReplicaWaitingToBeRecovered(
-        blocks[RWR].getLocalBlock(), vol, vol.createRbwFile(bpid,
-            blocks[RWR].getLocalBlock()).getParentFile()));
-    replicasMap.add(bpid, new ReplicaUnderRecovery(new FinalizedReplica(blocks[RUR]
-        .getLocalBlock(), vol, vol.getCurrentDir().getParentFile()), 2007));    
-    
+    try (FsDatasetSpi.FsVolumeReferences references =
+        dataSet.getFsVolumeReferences()) {
+      FsVolumeImpl vol = (FsVolumeImpl) references.get(0);
+      ReplicaInfo replicaInfo = new FinalizedReplica(
+          blocks[FINALIZED].getLocalBlock(), vol,
+          vol.getCurrentDir().getParentFile());
+      replicasMap.add(bpid, replicaInfo);
+      replicaInfo.getBlockFile().createNewFile();
+      replicaInfo.getMetaFile().createNewFile();
+
+      replicasMap.add(bpid, new ReplicaInPipeline(
+          blocks[TEMPORARY].getBlockId(),
+          blocks[TEMPORARY].getGenerationStamp(), vol,
+          vol.createTmpFile(bpid, blocks[TEMPORARY].getLocalBlock())
+              .getParentFile(), 0));
+
+      replicaInfo = new ReplicaBeingWritten(blocks[RBW].getLocalBlock(), vol,
+          vol.createRbwFile(bpid, blocks[RBW].getLocalBlock()).getParentFile(),
+          null);
+      replicasMap.add(bpid, replicaInfo);
+      replicaInfo.getBlockFile().createNewFile();
+      replicaInfo.getMetaFile().createNewFile();
+
+      replicasMap.add(bpid, new ReplicaWaitingToBeRecovered(
+          blocks[RWR].getLocalBlock(), vol, vol.createRbwFile(bpid,
+          blocks[RWR].getLocalBlock()).getParentFile()));
+      replicasMap
+          .add(bpid, new ReplicaUnderRecovery(new FinalizedReplica(blocks[RUR]
+              .getLocalBlock(), vol, vol.getCurrentDir().getParentFile()),
+              2007));
+    }
     return blocks;
   }
   
@@ -538,9 +546,15 @@ public class TestWriteToReplica {
           getFSDataset(dn);
       ReplicaMap replicaMap = dataSet.volumeMap;
       
-      List<FsVolumeImpl> volumes = dataSet.getVolumes();
-      // number of volumes should be 2 - [data1, data2]
-      assertEquals("number of volumes is wrong", 2, volumes.size());
+      List<FsVolumeImpl> volumes = null;
+      try (FsDatasetSpi.FsVolumeReferences referredVols = dataSet.getFsVolumeReferences()) {
+        // number of volumes should be 2 - [data1, data2]
+        assertEquals("number of volumes is wrong", 2, referredVols.size());
+        volumes = new ArrayList<>(referredVols.size());
+        for (FsVolumeSpi vol : referredVols) {
+          volumes.add((FsVolumeImpl) vol);
+        }
+      }
       ArrayList<String> bpList = new ArrayList<String>(Arrays.asList(
           cluster.getNamesystem(0).getBlockPoolId(), 
           cluster.getNamesystem(1).getBlockPoolId()));

http://git-wip-us.apache.org/repos/asf/hadoop/blob/24d3a2d4/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/mover/TestStorageMover.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/mover/TestStorageMover.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/mover/TestStorageMover.java
index a5d5848..d8b40d4 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/mover/TestStorageMover.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/mover/TestStorageMover.java
@@ -56,6 +56,7 @@ import org.apache.hadoop.hdfs.server.blockmanagement.BlockStoragePolicySuite;
 import org.apache.hadoop.hdfs.server.common.HdfsServerConstants;
 import org.apache.hadoop.hdfs.server.datanode.DataNode;
 import org.apache.hadoop.hdfs.server.datanode.DataNodeTestUtils;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.SnapshotTestHelper;
@@ -627,14 +628,18 @@ public class TestStorageMover {
   }
 
   private void setVolumeFull(DataNode dn, StorageType type) {
-    List<? extends FsVolumeSpi> volumes = dn.getFSDataset().getVolumes();
-    for (FsVolumeSpi v : volumes) {
-      FsVolumeImpl volume = (FsVolumeImpl) v;
-      if (volume.getStorageType() == type) {
-        LOG.info("setCapacity to 0 for [" + volume.getStorageType() + "]"
-            + volume.getStorageID());
-        volume.setCapacityForTesting(0);
+    try (FsDatasetSpi.FsVolumeReferences refs = dn.getFSDataset()
+        .getFsVolumeReferences()) {
+      for (FsVolumeSpi fvs : refs) {
+        FsVolumeImpl volume = (FsVolumeImpl) fvs;
+        if (volume.getStorageType() == type) {
+          LOG.info("setCapacity to 0 for [" + volume.getStorageType() + "]"
+              + volume.getStorageID());
+          volume.setCapacityForTesting(0);
+        }
       }
+    } catch (IOException e) {
+      LOG.error("Unexpected exception by closing FsVolumeReference", e);
     }
   }
 


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