diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 3352247e4a..1240edddb3 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -240,6 +240,8 @@ Release 2.0.3-alpha - Unreleased
     HDFS-3919. MiniDFSCluster:waitClusterUp can hang forever.
     (Andy Isaacson via eli)
 
+    HDFS-3924. Multi-byte id in HdfsVolumeId. (Andrew Wang via atm)
+
 Release 2.0.2-alpha - 2012-09-07 
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/fs/HdfsVolumeId.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/fs/HdfsVolumeId.java
index e283e52627..8e328051f7 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/fs/HdfsVolumeId.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/fs/HdfsVolumeId.java
@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.fs;
 
+import org.apache.commons.codec.binary.Base64;
 import org.apache.commons.lang.builder.EqualsBuilder;
 import org.apache.commons.lang.builder.HashCodeBuilder;
 import org.apache.hadoop.classification.InterfaceAudience;
@@ -31,10 +32,10 @@
 @InterfaceAudience.Public
 public class HdfsVolumeId implements VolumeId {
 
-  private final byte id;
+  private final byte[] id;
   private final boolean isValid;
 
-  public HdfsVolumeId(byte id, boolean isValid) {
+  public HdfsVolumeId(byte[] id, boolean isValid) {
     this.id = id;
     this.isValid = isValid;
   }
@@ -69,6 +70,6 @@ public boolean equals(Object obj) {
 
   @Override
   public String toString() {
-    return Byte.toString(id);
+    return Base64.encodeBase64String(id);
   }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockStorageLocationUtil.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockStorageLocationUtil.java
index e588864988..de74e02340 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockStorageLocationUtil.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockStorageLocationUtil.java
@@ -19,6 +19,7 @@
 package org.apache.hadoop.hdfs;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Iterator;
@@ -201,7 +202,7 @@ static Map<LocatedBlock, List<VolumeId>> associateVolumeIdsWithBlocks(
       ArrayList<VolumeId> l = new ArrayList<VolumeId>(b.getLocations().length);
       // Start off all IDs as invalid, fill it in later with results from RPCs
       for (int i = 0; i < b.getLocations().length; i++) {
-        l.add(new HdfsVolumeId((byte)-1, false));
+        l.add(new HdfsVolumeId(null, false));
       }
       blockVolumeIds.put(b, l);
     }
@@ -234,8 +235,8 @@ static Map<LocatedBlock, List<VolumeId>> associateVolumeIdsWithBlocks(
         }
         // Get the VolumeId by indexing into the list of VolumeIds
         // provided by the datanode
-        HdfsVolumeId id = new HdfsVolumeId(metaVolumeIds.get(volumeIndex)[0],
-            true);
+        byte[] volumeId = metaVolumeIds.get(volumeIndex);
+        HdfsVolumeId id = new HdfsVolumeId(volumeId, true);
         // Find out which index we are in the LocatedBlock's replicas
         LocatedBlock locBlock = extBlockToLocBlock.get(extBlock);
         DatanodeInfo[] dnInfos = locBlock.getLocations();
@@ -255,8 +256,8 @@ static Map<LocatedBlock, List<VolumeId>> associateVolumeIdsWithBlocks(
         }
         // Place VolumeId at the same index as the DN's index in the list of
         // replicas
-        List<VolumeId> VolumeIds = blockVolumeIds.get(locBlock);
-        VolumeIds.set(index, id);
+        List<VolumeId> volumeIds = blockVolumeIds.get(locBlock);
+        volumeIds.set(index, id);
       }
     }
     return blockVolumeIds;
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 d3f23c756d..0f9172247b 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
@@ -24,6 +24,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -1676,10 +1677,10 @@ public HdfsBlocksMetadata getHdfsBlocksMetadata(List<ExtendedBlock> blocks)
     List<byte[]> blocksVolumeIds = new ArrayList<byte[]>(volumes.volumes.size());
     // List of indexes into the list of VolumeIds, pointing at the VolumeId of
     // the volume that the block is on
-    List<Integer> blocksVolumendexes = new ArrayList<Integer>(blocks.size());
+    List<Integer> blocksVolumeIndexes = new ArrayList<Integer>(blocks.size());
     // Initialize the list of VolumeIds simply by enumerating the volumes
     for (int i = 0; i < volumes.volumes.size(); i++) {
-      blocksVolumeIds.add(new byte[] { (byte) i });
+      blocksVolumeIds.add(ByteBuffer.allocate(4).putInt(i).array());
     }
     // Determine the index of the VolumeId of each block's volume, by comparing 
     // the block's volume against the enumerated volumes
@@ -1700,10 +1701,10 @@ public HdfsBlocksMetadata getHdfsBlocksMetadata(List<ExtendedBlock> blocks)
       if (!isValid) {
         volumeIndex = Integer.MAX_VALUE;
       }
-      blocksVolumendexes.add(volumeIndex);
+      blocksVolumeIndexes.add(volumeIndex);
     }
     return new HdfsBlocksMetadata(blocks.toArray(new ExtendedBlock[] {}), 
-        blocksVolumeIds, blocksVolumendexes);
+        blocksVolumeIds, blocksVolumeIndexes);
   }
 
   @Override