HDFS-8204. Mover/Balancer should not schedule two replicas to the same datanode. Contributed by Walter Su

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -590,6 +590,9 @@ Release 2.7.1 - UNRELEASED
     HDFS-7931. DistributedFileSystem should not look for keyProvider in
     cache if Encryption is disabled (asuresh)
 
+    HDFS-8204. Mover/Balancer should not schedule two replicas to the same
+    datanode.  (Walter Su via szetszwo)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/balancer/Dispatcher.java

@@ -971,6 +971,9 @@ public static boolean waitForMoveCompletion(
    */
   private boolean isGoodBlockCandidate(StorageGroup source, StorageGroup target,
       StorageType targetStorageType, DBlock block) {
+    if (source.equals(target)) {
+      return false;
+    }
     if (target.storageType != targetStorageType) {
       return false;
     }
@@ -978,9 +981,19 @@ private boolean isGoodBlockCandidate(StorageGroup source, StorageGroup target,
     if (movedBlocks.contains(block.getBlock())) {
       return false;
     }
-    if (block.isLocatedOn(target)) {
+    final DatanodeInfo targetDatanode = target.getDatanodeInfo();
-      return false;
+    if (source.getDatanodeInfo().equals(targetDatanode)) {
+      // the block is moved inside same DN
+      return true;
     }
+
+    // check if block has replica in target node
+    for (StorageGroup blockLocation : block.getLocations()) {
+      if (blockLocation.getDatanodeInfo().equals(targetDatanode)) {
+        return false;
+      }
+    }
+
     if (cluster.isNodeGroupAware()
         && isOnSameNodeGroupWithReplicas(source, target, block)) {
       return false;

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/balancer/TestBalancer.java

@@ -48,6 +48,7 @@
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.StorageType;
+import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.hdfs.DFSClient;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.DFSTestUtil;
@@ -1307,6 +1308,68 @@ public void testBalancerWithRamDisk() throws Exception {
     }
   }
 
+  /**
+   * Test special case. Two replicas belong to same block should not in same node.
+   * We have 2 nodes.
+   * We have a block in (DN0,SSD) and (DN1,DISK).
+   * Replica in (DN0,SSD) should not be moved to (DN1,SSD).
+   * Otherwise DN1 has 2 replicas.
+   */
+  @Test(timeout=100000)
+  public void testTwoReplicaShouldNotInSameDN() throws Exception {
+    final Configuration conf = new HdfsConfiguration();
+
+    int blockSize = 5 * 1024 * 1024 ;
+    conf.setLong(DFSConfigKeys.DFS_BLOCK_SIZE_KEY, blockSize);
+    conf.setLong(DFSConfigKeys.DFS_HEARTBEAT_INTERVAL_KEY, 1L);
+    conf.setLong(DFSConfigKeys.DFS_NAMENODE_REPLICATION_INTERVAL_KEY, 1L);
+
+    int numOfDatanodes =2;
+    final MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf)
+        .numDataNodes(2)
+        .racks(new String[]{"/default/rack0", "/default/rack0"})
+        .storagesPerDatanode(2)
+        .storageTypes(new StorageType[][]{
+            {StorageType.SSD, StorageType.DISK},
+            {StorageType.SSD, StorageType.DISK}})
+        .storageCapacities(new long[][]{
+            {100 * blockSize, 20 * blockSize},
+            {20 * blockSize, 100 * blockSize}})
+        .build();
+
+    try {
+      cluster.waitActive();
+
+      //set "/bar" directory with ONE_SSD storage policy.
+      DistributedFileSystem fs = cluster.getFileSystem();
+      Path barDir = new Path("/bar");
+      fs.mkdir(barDir,new FsPermission((short)777));
+      fs.setStoragePolicy(barDir, HdfsConstants.ONESSD_STORAGE_POLICY_NAME);
+
+      // Insert 30 blocks. So (DN0,SSD) and (DN1,DISK) are about half full,
+      // and (DN0,SSD) and (DN1,DISK) are about 15% full.
+      long fileLen  = 30 * blockSize;
+      // fooFile has ONE_SSD policy. So
+      // (DN0,SSD) and (DN1,DISK) have 2 replicas belong to same block.
+      // (DN0,DISK) and (DN1,SSD) have 2 replicas belong to same block.
+      Path fooFile = new Path(barDir, "foo");
+      createFile(cluster, fooFile, fileLen, (short) numOfDatanodes, 0);
+      // update space info
+      cluster.triggerHeartbeats();
+
+      Balancer.Parameters p = Balancer.Parameters.DEFAULT;
+      Collection<URI> namenodes = DFSUtil.getNsServiceRpcUris(conf);
+      final int r = Balancer.run(namenodes, p, conf);
+
+      // Replica in (DN0,SSD) was not moved to (DN1,SSD), because (DN1,DISK)
+      // already has one. Otherwise DN1 will have 2 replicas.
+      // For same reason, no replicas were moved.
+      assertEquals(ExitStatus.NO_MOVE_PROGRESS.getExitCode(), r);
+
+    } finally {
+      cluster.shutdown();
+    }
+  }
   /**
    * @param args
    */