diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 21507f0b404..41e94bb604e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -125,6 +125,8 @@ Trunk (Unreleased)
 
     HDFS-6228. comments typo fix for FsDatasetImpl.java (zhaoyunjiong via umamahesh)
 
+    HDFS-6246. Remove 'dfs.support.append' flag from trunk code. (umamahesh)
+
   OPTIMIZATIONS
 
   BUG FIXES
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
index 58557c97d54..1d5e5bc5533 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
@@ -381,8 +381,6 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final int     DFS_NAMENODE_HANDLER_COUNT_DEFAULT = 10;
   public static final String  DFS_NAMENODE_SERVICE_HANDLER_COUNT_KEY = "dfs.namenode.service.handler.count";
   public static final int     DFS_NAMENODE_SERVICE_HANDLER_COUNT_DEFAULT = 10;
-  public static final String  DFS_SUPPORT_APPEND_KEY = "dfs.support.append";
-  public static final boolean DFS_SUPPORT_APPEND_DEFAULT = true;
   public static final String  DFS_HTTP_POLICY_KEY = "dfs.http.policy";
   public static final String  DFS_HTTP_POLICY_DEFAULT =  HttpConfig.Policy.HTTP_ONLY.name();
   public static final String  DFS_DEFAULT_CHUNK_VIEW_SIZE_KEY = "dfs.default.chunk.view.size";
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
index e47a302836d..6093339bdcb 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
@@ -95,12 +95,6 @@ class BlockPoolSlice {
       FileUtil.fullyDelete(tmpDir);
     }
     this.rbwDir = new File(currentDir, DataStorage.STORAGE_DIR_RBW);
-    final boolean supportAppends = conf.getBoolean(
-        DFSConfigKeys.DFS_SUPPORT_APPEND_KEY,
-        DFSConfigKeys.DFS_SUPPORT_APPEND_DEFAULT);
-    if (rbwDir.exists() && !supportAppends) {
-      FileUtil.fullyDelete(rbwDir);
-    }
     final int maxBlocksPerDir = conf.getInt(
         DFSConfigKeys.DFS_DATANODE_NUMBLOCKS_KEY,
         DFSConfigKeys.DFS_DATANODE_NUMBLOCKS_DEFAULT);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
index 508e9556546..16b356468a8 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
@@ -83,8 +83,6 @@
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_PERMISSIONS_SUPERUSERGROUP_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_REPLICATION_DEFAULT;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_REPLICATION_KEY;
-import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_SUPPORT_APPEND_DEFAULT;
-import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_SUPPORT_APPEND_KEY;
 import static org.apache.hadoop.util.Time.now;
 
 import java.io.BufferedWriter;
@@ -446,7 +444,6 @@ private void logAuditEvent(boolean succeeded,
   NameNodeResourceChecker nnResourceChecker;
 
   private final FsServerDefaults serverDefaults;
-  private final boolean supportAppends;
   private final ReplaceDatanodeOnFailure dtpReplaceDatanodeOnFailure;
 
   private volatile SafeModeInfo safeMode;  // safe mode information
@@ -754,8 +751,6 @@ static FSNamesystem loadFromDisk(Configuration conf) throws IOException {
           DFSConfigKeys.DFS_NAMENODE_MAX_BLOCKS_PER_FILE_DEFAULT);
       this.accessTimePrecision = conf.getLong(DFS_NAMENODE_ACCESSTIME_PRECISION_KEY,
           DFS_NAMENODE_ACCESSTIME_PRECISION_DEFAULT);
-      this.supportAppends = conf.getBoolean(DFS_SUPPORT_APPEND_KEY, DFS_SUPPORT_APPEND_DEFAULT);
-      LOG.info("Append Enabled: " + supportAppends);
 
       this.dtpReplaceDatanodeOnFailure = ReplaceDatanodeOnFailure.get(conf);
       
@@ -2597,12 +2592,6 @@ private LocatedBlock appendFileInt(String src, String holder,
           + ", clientMachine=" + clientMachine);
     }
     boolean skipSync = false;
-    if (!supportAppends) {
-      throw new UnsupportedOperationException(
-          "Append is not enabled on this NameNode. Use the " +
-          DFS_SUPPORT_APPEND_KEY + " configuration option to enable it.");
-    }
-
     LocatedBlock lb = null;
     FSPermissionChecker pc = getPermissionChecker();
     checkOperation(OperationCategory.WRITE);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestFileAppend.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestFileAppend.java
index 41feabb2abb..4ea534acdd6 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestFileAppend.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestFileAppend.java
@@ -345,7 +345,6 @@ public void testAppendAfterSoftLimit()
       throws IOException, InterruptedException {
     Configuration conf = new HdfsConfiguration();
     conf.setInt(DFSConfigKeys.DFS_REPLICATION_KEY, 1);
-    conf.setBoolean(DFSConfigKeys.DFS_SUPPORT_APPEND_KEY, true);
     //Set small soft-limit for lease
     final long softLimit = 1L;
     final long hardLimit = 9999999L;
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/fs/TestDFSIO.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/fs/TestDFSIO.java
index b354b204b8e..78f1ffa6841 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/fs/TestDFSIO.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/fs/TestDFSIO.java
@@ -201,7 +201,6 @@ private static Path getDataDir(Configuration conf) {
   @BeforeClass
   public static void beforeClass() throws Exception {
     bench = new TestDFSIO();
-    bench.getConf().setBoolean(DFSConfigKeys.DFS_SUPPORT_APPEND_KEY, true);
     cluster = new MiniDFSCluster.Builder(bench.getConf())
                                 .numDataNodes(2)
                                 .format(true)
@@ -733,7 +732,6 @@ else if(testType == TestType.TEST_TYPE_READ_SKIP && skipSize == 0)
 
     config.setInt("test.io.file.buffer.size", bufferSize);
     config.setLong("test.io.skip.size", skipSize);
-    config.setBoolean(DFSConfigKeys.DFS_SUPPORT_APPEND_KEY, true);
     FileSystem fs = FileSystem.get(config);
 
     if (isSequential) {