diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 7a9d0d6b28c..5c777e2b2fa 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -877,6 +877,9 @@ Release 0.23.0 - 2011-11-01
 
     HDFS-2130. Switch default checksum to CRC32C. (todd)
 
+    HDFS-2533. Remove needless synchronization on some FSDataSet methods.
+    (todd)
+
   BUG FIXES
 
     HDFS-2347. Fix checkpointTxnCount's comment about editlog size. 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/FSDataset.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/FSDataset.java
index 512d0b64bb0..e309dc1f475 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/FSDataset.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/FSDataset.java
@@ -1258,7 +1258,7 @@ public class FSDataset implements FSDatasetInterface {
   /**
    * Get File name for a given block.
    */
-  public synchronized File getBlockFile(String bpid, Block b)
+  public File getBlockFile(String bpid, Block b)
       throws IOException {
     File f = validateBlockFile(bpid, b);
     if(f == null) {
@@ -1271,16 +1271,44 @@ public class FSDataset implements FSDatasetInterface {
   }
   
   @Override // FSDatasetInterface
-  public synchronized InputStream getBlockInputStream(ExtendedBlock b)
+  public InputStream getBlockInputStream(ExtendedBlock b)
       throws IOException {
-    return new FileInputStream(getBlockFile(b));
+    File f = getBlockFileNoExistsCheck(b);
+    try {
+      return new FileInputStream(f);
+    } catch (FileNotFoundException fnfe) {
+      throw new IOException("Block " + b + " is not valid. " +
+          "Expected block file at " + f + " does not exist.");
+    }
+  }
+  
+  /**
+   * Return the File associated with a block, without first
+   * checking that it exists. This should be used when the
+   * next operation is going to open the file for read anyway,
+   * and thus the exists check is redundant.
+   */
+  private File getBlockFileNoExistsCheck(ExtendedBlock b)
+      throws IOException {
+    File f = getFile(b.getBlockPoolId(), b.getLocalBlock());
+    if (f == null) {
+      throw new IOException("Block " + b + " is not valid");
+    }
+    return f;
   }
 
   @Override // FSDatasetInterface
-  public synchronized InputStream getBlockInputStream(ExtendedBlock b,
+  public InputStream getBlockInputStream(ExtendedBlock b,
       long seekOffset) throws IOException {
-    File blockFile = getBlockFile(b);
-    RandomAccessFile blockInFile = new RandomAccessFile(blockFile, "r");
+    File blockFile = getBlockFileNoExistsCheck(b);
+    RandomAccessFile blockInFile;
+    try {
+      blockInFile = new RandomAccessFile(blockFile, "r");
+    } catch (FileNotFoundException fnfe) {
+      throw new IOException("Block " + b + " is not valid. " +
+          "Expected block file at " + blockFile + " does not exist.");
+    }
+
     if (seekOffset > 0) {
       blockInFile.seek(seekOffset);
     }