HDFS-2430. The number of failed or low-resource volumes the NN can tolerate should be configurable. Contributed by Aaron T. Myers

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1211650 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -21,6 +21,9 @@ Trunk (unreleased changes)
 
     HDFS-2636. Implement protobuf service for ClientDatanodeProtocol. (suresh)
 
+    HDFS-2430. The number of failed or low-resource volumes the NN can tolerate
+               should be configurable. (atm)
+
   IMPROVEMENTS
 
     HADOOP-7524 Change RPC to allow multiple protocols including multuple 

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -129,6 +129,8 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final boolean DFS_NAMENODE_SUPPORT_ALLOW_FORMAT_DEFAULT = true;
   public static final String  DFS_NAMENODE_NUM_CHECKPOINTS_RETAINED_KEY = "dfs.namenode.num.checkpoints.retained";
   public static final int     DFS_NAMENODE_NUM_CHECKPOINTS_RETAINED_DEFAULT = 2;
+  public static final String  DFS_NAMENODE_EDITS_DIR_MINIMUM_KEY = "dfs.namenode.edits.dir.minimum";
+  public static final int     DFS_NAMENODE_EDITS_DIR_MINIMUM_DEFAULT = 1;
   
   public static final String  DFS_LIST_LIMIT = "dfs.ls.limit";
   public static final int     DFS_LIST_LIMIT_DEFAULT = 1000;
@@ -162,6 +164,7 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final String  DFS_NAMENODE_NAME_DIR_KEY = "dfs.namenode.name.dir";
   public static final String  DFS_NAMENODE_EDITS_DIR_KEY = "dfs.namenode.edits.dir";
   public static final String  DFS_NAMENODE_EDITS_PLUGIN_PREFIX = "dfs.namenode.edits.journal-plugin";
+  public static final String  DFS_NAMENODE_EDITS_DIR_REQUIRED_KEY = "dfs.namenode.edits.dir.required";
   public static final String  DFS_CLIENT_READ_PREFETCH_SIZE_KEY = "dfs.client.read.prefetch.size"; 
   public static final String  DFS_CLIENT_RETRY_WINDOW_BASE= "dfs.client.retry.window.base";
   public static final String  DFS_METRICS_SESSION_ID_KEY = "dfs.metrics.session-id";
@@ -304,6 +307,8 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final String  DFS_NAMENODE_DU_RESERVED_KEY = "dfs.namenode.resource.du.reserved";
   public static final long    DFS_NAMENODE_DU_RESERVED_DEFAULT = 1024 * 1024 * 100; // 100 MB
   public static final String  DFS_NAMENODE_CHECKED_VOLUMES_KEY = "dfs.namenode.resource.checked.volumes";
+  public static final String  DFS_NAMENODE_CHECKED_VOLUMES_MINIMUM_KEY = "dfs.namenode.resource.checked.volumes.minimum";
+  public static final int     DFS_NAMENODE_CHECKED_VOLUMES_MINIMUM_DEFAULT = 1;
   public static final String  DFS_WEB_AUTHENTICATION_KERBEROS_PRINCIPAL_KEY = "dfs.web.authentication.kerberos.principal";
   public static final String  DFS_WEB_AUTHENTICATION_KERBEROS_KEYTAB_KEY = "dfs.web.authentication.kerberos.keytab";
   public static final String DFS_BLOCK_LOCAL_PATH_ACCESS_USER_KEY = "dfs.block.local-path-access.user";

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/Util.java

@@ -68,14 +68,28 @@ public static URI stringAsURI(String s) throws IOException {
   }
 
   /**
-   * Converts the passed File to a URI.
+   * Converts the passed File to a URI. This method trims the trailing slash if
+   * one is appended because the underlying file is in fact a directory that
+   * exists.
    * 
    * @param f the file to convert
    * @return the resulting URI
    * @throws IOException
    */
   public static URI fileAsURI(File f) throws IOException {
-    return f.getCanonicalFile().toURI();
+    URI u = f.getCanonicalFile().toURI();
+    
+    // trim the trailing slash, if it's present
+    if (u.getPath().endsWith("/")) {
+      String uriAsString = u.toString();
+      try {
+        u = new URI(uriAsString.substring(0, uriAsString.length() - 1));
+      } catch (URISyntaxException e) {
+        throw new IOException(e);
+      }
+    }
+    
+    return u;
   }
 
   /**

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/CheckableNameNodeResource.java

@@ -0,0 +1,45 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.namenode;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+/**
+ * Implementers of this class represent a NN resource whose availability can be
+ * checked. A resource can be either "required" or "redundant". All required
+ * resources must be available for the NN to continue operating. The NN will
+ * continue to operate as long as *any* redundant resource is available.
+ */
+@InterfaceAudience.Private
+interface CheckableNameNodeResource {
+  
+  /**
+   * Is this resource currently available. 
+   * 
+   * @return true if and only if the resource in question is available.  
+   */
+  public boolean isResourceAvailable();
+  
+  /**
+   * Is this resource required.
+   * 
+   * @return true if and only if the resource in question is required for NN operation.
+   */
+  public boolean isRequired();
+
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java

@@ -22,10 +22,10 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.lang.reflect.Constructor;
 
+import org.apache.commons.lang.StringUtils;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.classification.InterfaceAudience;
@@ -77,7 +77,7 @@ private enum State {
   private State state = State.UNINITIALIZED;
   
   //initialize
-  final private JournalSet journalSet;
+  private JournalSet journalSet;
   private EditLogOutputStream editLogStream = null;
 
   // a monotonically increasing counter that represents transactionIds.
@@ -112,6 +112,8 @@ private enum State {
   private NNStorage storage;
   private Configuration conf;
   
+  private Collection<URI> editsDirs;
+
   private static class TransactionId {
     public long txid;
 
@@ -127,19 +129,22 @@ protected synchronized TransactionId initialValue() {
     }
   };
 
-  final private Collection<URI> editsDirs;
-
   /**
    * Construct FSEditLog with default configuration, taking editDirs from NNStorage
+   * 
    * @param storage Storage object used by namenode
    */
   @VisibleForTesting
-  FSEditLog(NNStorage storage) {
+  FSEditLog(NNStorage storage) throws IOException {
-    this(new Configuration(), storage, Collections.<URI>emptyList());
+    Configuration conf = new Configuration();
+    // Make sure the edits dirs are set in the provided configuration object.
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
+        StringUtils.join(storage.getEditsDirectories(), ","));
+    init(conf, storage, FSNamesystem.getNamespaceEditsDirs(conf));
   }
 
   /**
-   * Constructor for FSEditLog. Add underlying journals are constructed, but 
+   * Constructor for FSEditLog. Underlying journals are constructed, but 
    * no streams are opened until open() is called.
    * 
    * @param conf The namenode configuration
@@ -147,36 +152,35 @@ protected synchronized TransactionId initialValue() {
    * @param editsDirs List of journals to use
    */
   FSEditLog(Configuration conf, NNStorage storage, Collection<URI> editsDirs) {
-    this.conf = conf;
+    init(conf, storage, editsDirs);
+  }
+  
+  private void init(Configuration conf, NNStorage storage, Collection<URI> editsDirs) {
     isSyncRunning = false;
+    this.conf = conf;
     this.storage = storage;
     metrics = NameNode.getNameNodeMetrics();
     lastPrintTime = now();
      
-    if (editsDirs.isEmpty()) { 
+    // If this list is empty, an error will be thrown on first use
-      // if this is the case, no edit dirs have been explictly configured
-      // image dirs are to be used for edits too
-      try {
-        editsDirs = Lists.newArrayList(storage.getEditsDirectories());
-      } catch (IOException ioe) {
-        // cannot get list from storage, so the empty editsDirs 
-        // will be assigned. an error will be thrown on first use
     // of the editlog, as no journals will exist
-      }
-      this.editsDirs = editsDirs;
-    } else {
     this.editsDirs = Lists.newArrayList(editsDirs);
-    }
     
-    this.journalSet = new JournalSet();
+    int minimumRedundantJournals = conf.getInt(
+        DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_MINIMUM_KEY,
+        DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_MINIMUM_DEFAULT);
+
+    journalSet = new JournalSet(minimumRedundantJournals);
     for (URI u : this.editsDirs) {
+      boolean required = FSNamesystem.getRequiredNamespaceEditsDirs(conf)
+          .contains(u);
       if (u.getScheme().equals(NNStorage.LOCAL_URI_SCHEME)) {
         StorageDirectory sd = storage.getStorageDirectory(u);
         if (sd != null) {
-          journalSet.add(new FileJournalManager(sd));
+          journalSet.add(new FileJournalManager(sd), required);
         }
       } else {
-        journalSet.add(createJournal(u));
+        journalSet.add(createJournal(u), required);
       }
     }
  
@@ -442,7 +446,7 @@ public void logSync() {
             }
             editLogStream.setReadyToFlush();
           } catch (IOException e) {
-            LOG.fatal("Could not sync any journal to persistent storage. "
+            LOG.fatal("Could not sync enough journals to persistent storage. "
                 + "Unsynced transactions: " + (txid - synctxid),
                 new Exception());
             runtime.exit(1);
@@ -464,7 +468,7 @@ public void logSync() {
         }
       } catch (IOException ex) {
         synchronized (this) {
-          LOG.fatal("Could not sync any journal to persistent storage. "
+          LOG.fatal("Could not sync enough journals to persistent storage. "
               + "Unsynced transactions: " + (txid - synctxid), new Exception());
           runtime.exit(1);
         }
@@ -917,7 +921,7 @@ synchronized void registerBackupNode(
     
     LOG.info("Registering new backup node: " + bnReg);
     BackupJournalManager bjm = new BackupJournalManager(bnReg, nnReg);
-    journalSet.add(bjm);
+    journalSet.add(bjm, true);
   }
   
   synchronized void releaseBackupStream(NamenodeRegistration registration)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java

@@ -738,7 +738,7 @@ void saveFSImage(SaveNamespaceContext context, StorageDirectory sd)
    * FSImageSaver assumes that it was launched from a thread that holds
    * FSNamesystem lock and waits for the execution of FSImageSaver thread
    * to finish.
-   * This way we are guraranteed that the namespace is not being updated
+   * This way we are guaranteed that the namespace is not being updated
    * while multiple instances of FSImageSaver are traversing it
    * and writing it out.
    */

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -33,6 +33,7 @@
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_DELEGATION_TOKEN_RENEW_INTERVAL_DEFAULT;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_DELEGATION_TOKEN_RENEW_INTERVAL_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_REQUIRED_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_MAX_OBJECTS_DEFAULT;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_MAX_OBJECTS_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY;
@@ -431,6 +432,21 @@ public static Collection<URI> getNamespaceDirs(Configuration conf) {
     return getStorageDirs(conf, DFS_NAMENODE_NAME_DIR_KEY);
   }
   
+  public static Collection<URI> getNamespaceEditsDirs(Configuration conf) {
+    Collection<URI> editsDirs = getStorageDirs(conf, DFS_NAMENODE_EDITS_DIR_KEY);
+    if (editsDirs.isEmpty()) {
+      // If this is the case, no edit dirs have been explicitly configured.
+      // Image dirs are to be used for edits too.
+      return getNamespaceDirs(conf);
+    } else {
+      return editsDirs;
+    }
+  }
+  
+  public static Collection<URI> getRequiredNamespaceEditsDirs(Configuration conf) {
+    return getStorageDirs(conf, DFS_NAMENODE_EDITS_DIR_REQUIRED_KEY);
+  }
+
   private static Collection<URI> getStorageDirs(Configuration conf,
                                                 String propertyName) {
     Collection<String> dirNames = conf.getTrimmedStringCollection(propertyName);
@@ -461,10 +477,6 @@ private static Collection<URI> getStorageDirs(Configuration conf,
     return Util.stringCollectionAsURIs(dirNames);
   }
 
-  public static Collection<URI> getNamespaceEditsDirs(Configuration conf) {
-    return getStorageDirs(conf, DFS_NAMENODE_EDITS_DIR_KEY);
-  }
-
   @Override
   public void readLock() {
     this.fsLock.readLock().lock();

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalSet.java

@@ -50,17 +50,16 @@ public class JournalSet implements JournalManager {
    * 
    * If a Journal gets disabled due to an error writing to its
    * stream, then the stream will be aborted and set to null.
-   * 
-   * This should be used outside JournalSet only for testing.
    */
-  @VisibleForTesting
+  static class JournalAndStream implements CheckableNameNodeResource {
-  static class JournalAndStream {
     private final JournalManager journal;
     private boolean disabled = false;
     private EditLogOutputStream stream;
+    private boolean required = false;
     
-    public JournalAndStream(JournalManager manager) {
+    public JournalAndStream(JournalManager manager, boolean required) {
       this.journal = manager;
+      this.required = required;
     }
 
     public void startLogSegment(long txId) throws IOException {
@@ -132,9 +131,24 @@ private boolean isDisabled() {
     private void setDisabled(boolean disabled) {
       this.disabled = disabled;
     }
+    
+    @Override
+    public boolean isResourceAvailable() {
+      return !isDisabled();
+    }
+    
+    @Override
+    public boolean isRequired() {
+      return required;
+    }
   }
   
   private List<JournalAndStream> journals = Lists.newArrayList();
+  final int minimumRedundantJournals;
+  
+  JournalSet(int minimumRedundantResources) {
+    this.minimumRedundantJournals = minimumRedundantResources;
+  }
   
   @Override
   public EditLogOutputStream startLogSegment(final long txId) throws IOException {
@@ -232,16 +246,15 @@ public long getNumberOfTransactions(long fromTxnId) throws IOException {
   }
 
   /**
-   * Returns true if there are no journals or all are disabled.
+   * Returns true if there are no journals, all redundant journals are disabled,
-   * @return True if no journals or all are disabled.
+   * or any required journals are disabled.
+   * 
+   * @return True if there no journals, all redundant journals are disabled,
+   * or any required journals are disabled.
    */
   public boolean isEmpty() {
-    for (JournalAndStream jas : journals) {
+    return !NameNodeResourcePolicy.areResourcesAvailable(journals,
-      if (!jas.isDisabled()) {
+        minimumRedundantJournals);
-        return false;
-      }
-    }
-    return true;
   }
   
   /**
@@ -292,9 +305,11 @@ private void mapJournalsAndReportErrors(
       }
     }
     disableAndReportErrorOnJournals(badJAS);
-    if (badJAS.size() >= journals.size()) {
+    if (!NameNodeResourcePolicy.areResourcesAvailable(journals,
-      LOG.error("Error: "+status+" failed for all journals");
+        minimumRedundantJournals)) {
-      throw new IOException(status+" failed on all the journals");
+      String message = status + " failed for too many journals";
+      LOG.error("Error: " + message);
+      throw new IOException(message);
     }
   }
   
@@ -450,8 +465,9 @@ List<JournalManager> getJournalManagers() {
     return jList;
   }
 
-  void add(JournalManager j) {
+  void add(JournalManager j, boolean required) {
-    journals.add(new JournalAndStream(j));
+    JournalAndStream jas = new JournalAndStream(j, required);
+    journals.add(jas);
   }
   
   void remove(JournalManager j) {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeResourceChecker.java

@@ -27,6 +27,7 @@
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.DF;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
@@ -40,29 +41,74 @@
  * 
  * NameNodeResourceChecker provides a method -
  * <code>hasAvailableDiskSpace</code> - which will return true if and only if
- * the NameNode has disk space available on all volumes which are configured to
+ * the NameNode has disk space available on all required volumes, and any volume
- * be checked. Volumes containing file system name/edits dirs are added by
+ * which is configured to be redundant. Volumes containing file system edits dirs
- * default, and arbitrary extra volumes may be configured as well.
+ * are added by default, and arbitrary extra volumes may be configured as well.
  */
-public class NameNodeResourceChecker {
+@InterfaceAudience.Private
+class NameNodeResourceChecker {
   private static final Log LOG = LogFactory.getLog(NameNodeResourceChecker.class.getName());
 
   // Space (in bytes) reserved per volume.
   private long duReserved;
 
   private final Configuration conf;
-  private Map<String, DF> volumes;
+  private Map<String, CheckedVolume> volumes;
+  private int minimumRedundantVolumes;
+  
+  @VisibleForTesting
+  class CheckedVolume implements CheckableNameNodeResource {
+    private DF df;
+    private boolean required;
+    private String volume;
+    
+    public CheckedVolume(File dirToCheck, boolean required)
+        throws IOException {
+      df = new DF(dirToCheck, conf);
+      this.required = required;
+      volume = df.getFilesystem();
+    }
+    
+    public String getVolume() {
+      return volume;
+    }
+    
+    @Override
+    public boolean isRequired() {
+      return required;
+    }
+
+    @Override
+    public boolean isResourceAvailable() {
+      long availableSpace = df.getAvailable();
+      if (LOG.isDebugEnabled()) {
+        LOG.debug("Space available on volume '" + volume + "' is "
+            + availableSpace);
+      }
+      if (availableSpace < duReserved) {
+        LOG.warn("Space available on volume '" + volume + "' is "
+            + availableSpace +
+            ", which is below the configured reserved amount " + duReserved);
+        return false;
+      } else {
+        return true;
+      }
+    }
+    
+    @Override
+    public String toString() {
+      return "volume: " + volume + " required: " + required +
+          " resource available: " + isResourceAvailable();
+    }
+  }
 
   /**
-   * Create a NameNodeResourceChecker, which will check the name dirs and edits
+   * Create a NameNodeResourceChecker, which will check the edits dirs and any
-   * dirs set in <code>conf</code>.
+   * additional dirs to check set in <code>conf</code>.
-   * 
-   * @param conf
-   * @throws IOException
    */
   public NameNodeResourceChecker(Configuration conf) throws IOException {
     this.conf = conf;
-    volumes = new HashMap<String, DF>();
+    volumes = new HashMap<String, CheckedVolume>();
 
     duReserved = conf.getLong(DFSConfigKeys.DFS_NAMENODE_DU_RESERVED_KEY,
         DFSConfigKeys.DFS_NAMENODE_DU_RESERVED_DEFAULT);
@@ -70,8 +116,6 @@ public NameNodeResourceChecker(Configuration conf) throws IOException {
     Collection<URI> extraCheckedVolumes = Util.stringCollectionAsURIs(conf
         .getTrimmedStringCollection(DFSConfigKeys.DFS_NAMENODE_CHECKED_VOLUMES_KEY));
     
-    addDirsToCheck(FSNamesystem.getNamespaceDirs(conf));
-    
     Collection<URI> localEditDirs = Collections2.filter(
         FSNamesystem.getNamespaceEditsDirs(conf),
         new Predicate<URI>() {
@@ -82,70 +126,86 @@ public boolean apply(URI input) {
             return false;
           }
         });
-    addDirsToCheck(localEditDirs);
+
-    addDirsToCheck(extraCheckedVolumes);
+    // Add all the local edits dirs, marking some as required if they are
+    // configured as such.
+    for (URI editsDirToCheck : localEditDirs) {
+      addDirToCheck(editsDirToCheck,
+          FSNamesystem.getRequiredNamespaceEditsDirs(conf).contains(
+              editsDirToCheck));
+    }
+
+    // All extra checked volumes are marked "required"
+    for (URI extraDirToCheck : extraCheckedVolumes) {
+      addDirToCheck(extraDirToCheck, true);
+    }
+    
+    minimumRedundantVolumes = conf.getInt(
+        DFSConfigKeys.DFS_NAMENODE_CHECKED_VOLUMES_MINIMUM_KEY,
+        DFSConfigKeys.DFS_NAMENODE_CHECKED_VOLUMES_MINIMUM_DEFAULT);
   }
 
   /**
-   * Add the passed-in directories to the list of volumes to check.
+   * Add the volume of the passed-in directory to the list of volumes to check.
+   * If <code>required</code> is true, and this volume is already present, but
+   * is marked redundant, it will be marked required. If the volume is already
+   * present but marked required then this method is a no-op.
    * 
-   * @param directoriesToCheck
+   * @param directoryToCheck
-   *          The directories whose volumes will be checked for available space.
+   *          The directory whose volume will be checked for available space.
-   * @throws IOException
    */
-  private void addDirsToCheck(Collection<URI> directoriesToCheck)
+  private void addDirToCheck(URI directoryToCheck, boolean required)
       throws IOException {
-    for (URI directoryUri : directoriesToCheck) {
+    File dir = new File(directoryToCheck.getPath());
-      File dir = new File(directoryUri.getPath());
     if (!dir.exists()) {
       throw new IOException("Missing directory "+dir.getAbsolutePath());
     }
-      DF df = new DF(dir, conf);
+    
-      volumes.put(df.getFilesystem(), df);
+    CheckedVolume newVolume = new CheckedVolume(dir, required);
+    CheckedVolume volume = volumes.get(newVolume.getVolume());
+    if (volume == null || (volume != null && !volume.isRequired())) {
+      volumes.put(newVolume.getVolume(), newVolume);
     }
   }
 
   /**
    * Return true if disk space is available on at least one of the configured
-   * volumes.
+   * redundant volumes, and all of the configured required volumes.
    * 
    * @return True if the configured amount of disk space is available on at
-   *         least one volume, false otherwise.
+   *         least one redundant volume and all of the required volumes, false
-   * @throws IOException
+   *         otherwise.
    */
   boolean hasAvailableDiskSpace()
       throws IOException {
-    return getVolumesLowOnSpace().size() < volumes.size();
+    return NameNodeResourcePolicy.areResourcesAvailable(volumes.values(),
+        minimumRedundantVolumes);
   }
 
   /**
    * Return the set of directories which are low on space.
+   * 
    * @return the set of directories whose free space is below the threshold.
-   * @throws IOException 
    */
+  @VisibleForTesting
   Collection<String> getVolumesLowOnSpace() throws IOException {
     if (LOG.isDebugEnabled()) {
       LOG.debug("Going to check the following volumes disk space: " + volumes);
     }
     Collection<String> lowVolumes = new ArrayList<String>();
-    for (DF volume : volumes.values()) {
+    for (CheckedVolume volume : volumes.values()) {
-      long availableSpace = volume.getAvailable();
+      lowVolumes.add(volume.getVolume());
-      String fileSystem = volume.getFilesystem();
-      if (LOG.isDebugEnabled()) {
-        LOG.debug("Space available on volume '" + fileSystem + "' is " + availableSpace);
-      }
-      if (availableSpace < duReserved) {
-        LOG.warn("Space available on volume '" + fileSystem + "' is "
-            + availableSpace +
-            ", which is below the configured reserved amount " + duReserved);
-        lowVolumes.add(volume.getFilesystem());
-      }
     }
     return lowVolumes;
   }
   
   @VisibleForTesting
-  void setVolumes(Map<String, DF> volumes) {
+  void setVolumes(Map<String, CheckedVolume> volumes) {
     this.volumes = volumes;
   }
+  
+  @VisibleForTesting
+  void setMinimumReduntdantVolumes(int minimumRedundantVolumes) {
+    this.minimumRedundantVolumes = minimumRedundantVolumes;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeResourcePolicy.java

@@ -0,0 +1,81 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.namenode;
+
+import java.util.Collection;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+/**
+ * Given a set of checkable resources, this class is capable of determining
+ * whether sufficient resources are available for the NN to continue operating.
+ */
+@InterfaceAudience.Private
+final class NameNodeResourcePolicy {
+
+  /**
+   * Return true if and only if there are sufficient NN
+   * resources to continue logging edits.
+   * 
+   * @param resources the collection of resources to check.
+   * @param minimumRedundantResources the minimum number of redundant resources
+   *        required to continue operation.
+   * @return true if and only if there are sufficient NN resources to
+   *         continue logging edits.
+   * @throws RuntimeException if the number of <bold>configured</bold>
+   *         redundant resources is fewer than the minimum number of available
+   *         redundant resources.
+   */
+  static boolean areResourcesAvailable(
+      Collection<? extends CheckableNameNodeResource> resources,
+      int minimumRedundantResources) {
+    
+    int requiredResourceCount = 0;
+    int redundantResourceCount = 0;
+    int disabledRedundantResourceCount = 0;
+    for (CheckableNameNodeResource resource : resources) {
+      if (!resource.isRequired()) {
+        redundantResourceCount++;
+        if (!resource.isResourceAvailable()) {
+          disabledRedundantResourceCount++;
+        }
+      } else {
+        requiredResourceCount++;
+        if (!resource.isResourceAvailable()) {
+          // Short circuit - a required resource is not available.
+          return false;
+        }
+      }
+    }
+    
+    if (redundantResourceCount < minimumRedundantResources) {
+      throw new RuntimeException("Need a minimum of " + minimumRedundantResources
+          + " for NN to operate but only " + redundantResourceCount
+          + " are configured.");
+    }
+    
+    if (redundantResourceCount == 0) {
+      // If there are no redundant resources, return true if there are any
+      // required resources available.
+      return requiredResourceCount > 0;
+    } else {
+      return redundantResourceCount - disabledRedundantResourceCount >=
+          minimumRedundantResources;
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestClusterId.java

@@ -47,7 +47,7 @@ public class TestClusterId {
   private String getClusterId(Configuration config) throws IOException {
     // see if cluster id not empty.
     Collection<URI> dirsToFormat = FSNamesystem.getNamespaceDirs(config);
-    Collection<URI> editsToFormat = new ArrayList<URI>(0);
+    Collection<URI> editsToFormat = FSNamesystem.getNamespaceEditsDirs(config);
     FSImage fsImage = new FSImage(config, dirsToFormat, editsToFormat);
     
     Iterator<StorageDirectory> sdit = 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLogJournalFailures.java

@@ -21,28 +21,32 @@
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Matchers.anyInt;
 import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.atLeast;
 import static org.mockito.Mockito.doNothing;
 import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 
+import java.io.File;
 import java.io.IOException;
 
+import org.apache.commons.lang.StringUtils;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.HdfsConfiguration;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.hdfs.server.namenode.JournalSet.JournalAndStream;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
+import org.mockito.verification.VerificationMode;
 
 public class TestEditLogJournalFailures {
 
   private int editsPerformed = 0;
-  private Configuration conf;
   private MiniDFSCluster cluster;
   private FileSystem fs;
   private Runtime runtime;
@@ -53,8 +57,13 @@ public class TestEditLogJournalFailures {
    */
   @Before
   public void setUpMiniCluster() throws IOException {
-    conf = new HdfsConfiguration();
+    setUpMiniCluster(new HdfsConfiguration(), true);
-    cluster = new MiniDFSCluster.Builder(conf).numDataNodes(0).build();
+  }
+  
+  public void setUpMiniCluster(Configuration conf, boolean manageNameDfsDirs)
+      throws IOException {
+    cluster = new MiniDFSCluster.Builder(conf).numDataNodes(0)
+        .manageNameDfsDirs(manageNameDfsDirs).build();
     cluster.waitActive();
     fs = cluster.getFileSystem();
     
@@ -67,7 +76,9 @@ public void setUpMiniCluster() throws IOException {
   
   @After
   public void shutDownMiniCluster() throws IOException {
+    if (fs != null)
       fs.close();
+    if (cluster != null)
       cluster.shutdown();
   }
    
@@ -109,7 +120,7 @@ public void testAllEditsDirFailOnWrite() throws IOException {
     assertTrue(doAnEdit());
     // The previous edit could not be synced to any persistent storage, should
     // have halted the NN.
-    assertExitInvocations(1);
+    assertExitInvocations(atLeast(1));
   }
   
   @Test
@@ -125,6 +136,80 @@ public void testSingleFailedEditsDirOnSetReadyToFlush() throws IOException {
     assertFalse(cluster.getNameNode().isInSafeMode());
   }
   
+  @Test
+  public void testSingleRequiredFailedEditsDirOnSetReadyToFlush()
+      throws IOException {
+    // Set one of the edits dirs to be required.
+    String[] editsDirs = cluster.getConfiguration(0).getTrimmedStrings(
+        DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY);
+    shutDownMiniCluster();
+    Configuration conf = new HdfsConfiguration();
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_REQUIRED_KEY, editsDirs[1]);
+    conf.setInt(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_MINIMUM_KEY, 0);
+    conf.setInt(DFSConfigKeys.DFS_NAMENODE_CHECKED_VOLUMES_MINIMUM_KEY, 0);
+    setUpMiniCluster(conf, true);
+    
+    assertTrue(doAnEdit());
+    // Invalidated the one required edits journal.
+    invalidateEditsDirAtIndex(1, false, false);
+    // Make sure runtime.exit(...) hasn't been called at all yet.
+    assertExitInvocations(0);
+    
+    // This will actually return true in the tests, since the NN will not in
+    // fact call Runtime.exit();
+    doAnEdit();
+    
+    // A single failure of a required journal should result in a call to
+    // runtime.exit(...).
+    assertExitInvocations(atLeast(1));
+  }
+  
+  @Test
+  public void testMultipleRedundantFailedEditsDirOnSetReadyToFlush()
+      throws IOException {
+    // Set up 4 name/edits dirs.
+    shutDownMiniCluster();
+    Configuration conf = new HdfsConfiguration();
+    String[] nameDirs = new String[4];
+    for (int i = 0; i < nameDirs.length; i++) {
+      File nameDir = new File(System.getProperty("test.build.data"),
+          "name-dir" + i);
+      nameDir.mkdirs();
+      nameDirs[i] = nameDir.getAbsolutePath();
+    }
+    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY,
+        StringUtils.join(nameDirs, ","));
+    
+    // Keep running unless there are less than 2 edits dirs remaining.
+    conf.setInt(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_MINIMUM_KEY, 2);
+    setUpMiniCluster(conf, false);
+    
+    // All journals active.
+    assertTrue(doAnEdit());
+    assertExitInvocations(0);
+    
+    // Invalidate 1/4 of the redundant journals.
+    invalidateEditsDirAtIndex(0, false, false);
+    assertTrue(doAnEdit());
+    assertExitInvocations(0);
+
+    // Invalidate 2/4 of the redundant journals.
+    invalidateEditsDirAtIndex(1, false, false);
+    assertTrue(doAnEdit());
+    assertExitInvocations(0);
+    
+    // Invalidate 3/4 of the redundant journals.
+    invalidateEditsDirAtIndex(2, false, false);
+    
+    // This will actually return true in the tests, since the NN will not in
+    // fact call Runtime.exit();
+    doAnEdit();
+    
+    // A failure of more than the minimum number of redundant journals should
+    // result in a call to runtime.exit(...).
+    assertExitInvocations(atLeast(1));
+  }
+
   /**
    * Replace the journal at index <code>index</code> with one that throws an
    * exception on flush.
@@ -182,13 +267,24 @@ private boolean doAnEdit() throws IOException {
     return fs.mkdirs(new Path("/tmp", Integer.toString(editsPerformed++)));
   }
   
+  /**
+   * Make sure that Runtime.exit(...) has been called exactly
+   * <code>expectedExits<code> number of times.
+   * 
+   * @param expectedExits the exact number of times Runtime.exit(...) should
+   *                      have been called.
+   */
+  private void assertExitInvocations(int expectedExits) {
+    assertExitInvocations(times(expectedExits));
+  }
+
   /**
    * Make sure that Runtime.exit(...) has been called
    * <code>expectedExits<code> number of times.
    * 
    * @param expectedExits the number of times Runtime.exit(...) should have been called.
    */
-  private void assertExitInvocations(int expectedExits) {
+  private void assertExitInvocations(VerificationMode expectedExits) {
-    verify(runtime, times(expectedExits)).exit(anyInt());
+    verify(runtime, expectedExits).exit(anyInt());
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestGenericJournalConf.java

@@ -118,6 +118,7 @@ public void testDummyJournalManager() throws Exception {
              DummyJournalManager.class.getName());
     conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
              "dummy://test");
+    conf.setInt(DFSConfigKeys.DFS_NAMENODE_CHECKED_VOLUMES_MINIMUM_KEY, 0);
     try {
       cluster = new MiniDFSCluster.Builder(conf).numDataNodes(0).build();
       cluster.waitActive();

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestNameNodeResourceChecker.java

@@ -19,21 +19,20 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.net.URISyntaxException;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
 
 import org.apache.hadoop.conf.Configuration;
-import org.apache.hadoop.fs.DF;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.hdfs.server.namenode.FSNamesystem.NameNodeResourceMonitor;
+import org.apache.hadoop.hdfs.server.namenode.NameNodeResourceChecker.CheckedVolume;
 import org.junit.Before;
 import org.junit.Test;
 import org.mockito.Mockito;
 
-import com.google.common.collect.Lists;
-
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
@@ -49,7 +48,7 @@ public void setUp () throws IOException {
     baseDir = new File(System.getProperty("test.build.data"));
     nameDir = new File(baseDir, "resource-check-name-dir");
     nameDir.mkdirs();
-    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY, nameDir.getAbsolutePath());
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY, nameDir.getAbsolutePath());
   }
 
   /**
@@ -90,7 +89,7 @@ public void testCheckThatNameNodeResourceMonitorIsRunning()
       throws IOException, InterruptedException {
     MiniDFSCluster cluster = null;
     try {
-      conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY, nameDir.getAbsolutePath());
+      conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY, nameDir.getAbsolutePath());
       conf.setLong(DFSConfigKeys.DFS_NAMENODE_RESOURCE_CHECK_INTERVAL_KEY, 1);
       
       cluster = new MiniDFSCluster.Builder(conf)
@@ -145,7 +144,7 @@ public void testChecking2NameDirsOnOneVolume() throws IOException {
     File nameDir2 = new File(System.getProperty("test.build.data"), "name-dir2");
     nameDir1.mkdirs();
     nameDir2.mkdirs();
-    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY,
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
         nameDir1.getAbsolutePath() + "," + nameDir2.getAbsolutePath());
     conf.setLong(DFSConfigKeys.DFS_NAMENODE_DU_RESERVED_KEY, Long.MAX_VALUE);
 
@@ -164,7 +163,7 @@ public void testCheckingExtraVolumes() throws IOException {
     Configuration conf = new Configuration();
     File nameDir = new File(System.getProperty("test.build.data"), "name-dir");
     nameDir.mkdirs();
-    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY, nameDir.getAbsolutePath());
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY, nameDir.getAbsolutePath());
     conf.set(DFSConfigKeys.DFS_NAMENODE_CHECKED_VOLUMES_KEY, nameDir.getAbsolutePath());
     conf.setLong(DFSConfigKeys.DFS_NAMENODE_DU_RESERVED_KEY, Long.MAX_VALUE);
 
@@ -176,38 +175,70 @@ public void testCheckingExtraVolumes() throws IOException {
 
   /**
    * Test that the NN is considered to be out of resources only once all
-   * configured volumes are low on resources.
+   * redundant configured volumes are low on resources, or when any required
+   * volume is low on resources. 
    */
   @Test
-  public void testLowResourceVolumePolicy() throws IOException {
+  public void testLowResourceVolumePolicy() throws IOException, URISyntaxException {
     Configuration conf = new Configuration();
     File nameDir1 = new File(System.getProperty("test.build.data"), "name-dir1");
     File nameDir2 = new File(System.getProperty("test.build.data"), "name-dir2");
     nameDir1.mkdirs();
     nameDir2.mkdirs();
     
-    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY,
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
         nameDir1.getAbsolutePath() + "," + nameDir2.getAbsolutePath());
+    conf.setInt(DFSConfigKeys.DFS_NAMENODE_CHECKED_VOLUMES_MINIMUM_KEY, 2);
     
     NameNodeResourceChecker nnrc = new NameNodeResourceChecker(conf);
     
     // For the purpose of this test, we need to force the name dirs to appear to
     // be on different volumes.
-    Map<String, DF> volumes = new HashMap<String, DF>();
+    Map<String, CheckedVolume> volumes = new HashMap<String, CheckedVolume>();
-    volumes.put("volume1", new DF(nameDir1, conf));
+    CheckedVolume volume1 = Mockito.mock(CheckedVolume.class);
-    volumes.put("volume2", new DF(nameDir2, conf));
+    CheckedVolume volume2 = Mockito.mock(CheckedVolume.class);
+    CheckedVolume volume3 = Mockito.mock(CheckedVolume.class);
+    CheckedVolume volume4 = Mockito.mock(CheckedVolume.class);
+    CheckedVolume volume5 = Mockito.mock(CheckedVolume.class);
+    Mockito.when(volume1.isResourceAvailable()).thenReturn(true);
+    Mockito.when(volume2.isResourceAvailable()).thenReturn(true);
+    Mockito.when(volume3.isResourceAvailable()).thenReturn(true);
+    Mockito.when(volume4.isResourceAvailable()).thenReturn(true);
+    Mockito.when(volume5.isResourceAvailable()).thenReturn(true);
+    
+    // Make volumes 4 and 5 required.
+    Mockito.when(volume4.isRequired()).thenReturn(true);
+    Mockito.when(volume5.isRequired()).thenReturn(true);
+    
+    volumes.put("volume1", volume1);
+    volumes.put("volume2", volume2);
+    volumes.put("volume3", volume3);
+    volumes.put("volume4", volume4);
+    volumes.put("volume5", volume5);
     nnrc.setVolumes(volumes);
     
-    NameNodeResourceChecker spyNnrc = Mockito.spy(nnrc);
+    // Initially all dirs have space.
+    assertTrue(nnrc.hasAvailableDiskSpace());
     
-    Mockito.when(spyNnrc.getVolumesLowOnSpace()).thenReturn(
+    // 1/3 redundant dir is low on space.
-        Lists.newArrayList("volume1"));
+    Mockito.when(volume1.isResourceAvailable()).thenReturn(false);
+    assertTrue(nnrc.hasAvailableDiskSpace());
     
-    assertTrue(spyNnrc.hasAvailableDiskSpace());
+    // 2/3 redundant dirs are low on space.
+    Mockito.when(volume2.isResourceAvailable()).thenReturn(false);
+    assertFalse(nnrc.hasAvailableDiskSpace());
     
-    Mockito.when(spyNnrc.getVolumesLowOnSpace()).thenReturn(
+    // Lower the minimum number of redundant volumes that must be available.
-        Lists.newArrayList("volume1", "volume2"));
+    nnrc.setMinimumReduntdantVolumes(1);
+    assertTrue(nnrc.hasAvailableDiskSpace());
     
-    assertFalse(spyNnrc.hasAvailableDiskSpace());
+    // Just one required dir is low on space.
+    Mockito.when(volume3.isResourceAvailable()).thenReturn(false);
+    assertFalse(nnrc.hasAvailableDiskSpace());
+    
+    // Just the other required dir is low on space.
+    Mockito.when(volume3.isResourceAvailable()).thenReturn(true);
+    Mockito.when(volume4.isResourceAvailable()).thenReturn(false);
+    assertFalse(nnrc.hasAvailableDiskSpace());
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestNameNodeResourcePolicy.java

@@ -0,0 +1,107 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.namenode;
+
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import java.util.ArrayList;
+import java.util.Collection;
+
+import org.junit.Test;
+
+public class TestNameNodeResourcePolicy {
+
+  @Test
+  public void testSingleRedundantResource() {
+    assertTrue(testResourceScenario(1, 0, 0, 0, 1));
+    assertFalse(testResourceScenario(1, 0, 1, 0, 1));
+  }
+  
+  @Test
+  public void testSingleRequiredResource() {
+    assertTrue(testResourceScenario(0, 1, 0, 0, 0));
+    assertFalse(testResourceScenario(0, 1, 0, 1, 0));
+  }
+  
+  @Test
+  public void testMultipleRedundantResources() {
+    assertTrue(testResourceScenario(4, 0, 0, 0, 4));
+    assertFalse(testResourceScenario(4, 0, 1, 0, 4));
+    assertTrue(testResourceScenario(4, 0, 1, 0, 3));
+    assertFalse(testResourceScenario(4, 0, 2, 0, 3));
+    assertTrue(testResourceScenario(4, 0, 2, 0, 2));
+    assertFalse(testResourceScenario(4, 0, 3, 0, 2));
+    assertTrue(testResourceScenario(4, 0, 3, 0, 1));
+    assertFalse(testResourceScenario(4, 0, 4, 0, 1));
+    try {
+      testResourceScenario(1, 0, 0, 0, 2);
+      fail("Should fail if there are more minimum redundant resources than " +
+          "total redundant resources");
+    } catch (RuntimeException rte) {
+      assertTrue(rte.getMessage().startsWith("Need a minimum"));
+    }
+  }
+  
+  @Test
+  public void testMultipleRequiredResources() {
+    assertTrue(testResourceScenario(0, 3, 0, 0, 0));
+    assertFalse(testResourceScenario(0, 3, 0, 1, 0));
+    assertFalse(testResourceScenario(0, 3, 0, 2, 0));
+    assertFalse(testResourceScenario(0, 3, 0, 3, 0));
+  }
+  
+  @Test
+  public void testRedundantWithRequiredResources() {
+    assertTrue(testResourceScenario(2, 2, 0, 0, 1));
+    assertTrue(testResourceScenario(2, 2, 1, 0, 1));
+    assertFalse(testResourceScenario(2, 2, 2, 0, 1));
+    assertFalse(testResourceScenario(2, 2, 0, 1, 1));
+    assertFalse(testResourceScenario(2, 2, 1, 1, 1));
+    assertFalse(testResourceScenario(2, 2, 2, 1, 1));
+  }
+  
+  private static boolean testResourceScenario(
+      int numRedundantResources,
+      int numRequiredResources,
+      int numFailedRedundantResources,
+      int numFailedRequiredResources,
+      int minimumRedundantResources) {
+    
+    Collection<CheckableNameNodeResource> resources =
+        new ArrayList<CheckableNameNodeResource>();
+    
+    for (int i = 0; i < numRedundantResources; i++) {
+      CheckableNameNodeResource r = mock(CheckableNameNodeResource.class);
+      when(r.isRequired()).thenReturn(false);
+      when(r.isResourceAvailable()).thenReturn(i >= numFailedRedundantResources);
+      resources.add(r);
+    }
+    
+    for (int i = 0; i < numRequiredResources; i++) {
+      CheckableNameNodeResource r = mock(CheckableNameNodeResource.class);
+      when(r.isRequired()).thenReturn(true);
+      when(r.isResourceAvailable()).thenReturn(i >= numFailedRequiredResources);
+      resources.add(r);
+    }
+    
+    return NameNodeResourcePolicy.areResourcesAvailable(resources,
+        minimumRedundantResources);    
+  }
+}