Adding a new namenode data directory to an existing cluster

Question

What procedure do i need to follow to properly add a new NameNode data directory (dfs.name.dir, dfs.namenode.name.dir) to an existing production cluster? I have added the new path to the comma-delimited list in the hdfs-site.xml file but when i try to start the namenode i get the following error:

Directory /data/nfs/dfs/nn is in an inconsistent state: storage directory does not exist or is not accessible.

In my case, i have two directories already in place and working. (/data/1/dfs/nn,/data/2/dfs/nn) When i add the new directory I can't start the namenode. When the new path is removed, it starts just fine. My fstab for the new directory looks like this:

backup-server:/hadoop_nn /data/nfs/dfs nfs tcp,soft,intr,timeo=10,retrans=10 1 2

In the above mount point I have created a folder called nn. That folder has identical ownership and permissions to the other two existing locations nn folder.

drwx------ 2 hdfs hadoop 64 Jan 22 16:30 nn

Do i need to manually replicate/copy all the files from one of the existing namenode directories or should the namenode service do that automatically when it's started?

Answer 1

I believe i may have just answered my own question. I ended up copying the entire contents of one of the existing namenode directories over to the new NFS namenode directory and i was able to start the namenode. (Note that i stopped the namenode before copying to avoid problems)

cp -rp /data/1/dfs/nn /data/nfs/dfs/nn

I guess my assumption that the namenode would automatically copy the existing metadata over to the new directory was incorrect.

Answer 2

In Cloudera CDH 4.5.0, that error can only occur when the following function (from Storage.java, around line 418) returns NON_EXISTENT. It appears in each case a warning is logged with more details, look for log lines from org.apache.hadoop.hdfs.server.common.Storage.

In short, it appears the name node perceives it to not exist, not be a directory, not writable or otherwise threw a SecurityException.

/**
 * Check consistency of the storage directory
 * 
 * @param startOpt a startup option.
 *  
 * @return state {@link StorageState} of the storage directory 
 * @throws InconsistentFSStateException if directory state is not 
 * consistent and cannot be recovered.
 * @throws IOException
 */
public StorageState analyzeStorage(StartupOption startOpt, Storage storage)
    throws IOException {
  assert root != null : "root is null";
  String rootPath = root.getCanonicalPath();
  try { // check that storage exists
    if (!root.exists()) {
      // storage directory does not exist
      if (startOpt != StartupOption.FORMAT) {
        LOG.warn("Storage directory " + rootPath + " does not exist");
        return StorageState.NON_EXISTENT;
      }
      LOG.info(rootPath + " does not exist. Creating ...");
      if (!root.mkdirs())
        throw new IOException("Cannot create directory " + rootPath);
    }
    // or is inaccessible
    if (!root.isDirectory()) {
      LOG.warn(rootPath + "is not a directory");
      return StorageState.NON_EXISTENT;
    }
    if (!root.canWrite()) {
      LOG.warn("Cannot access storage directory " + rootPath);
      return StorageState.NON_EXISTENT;
    }
  } catch(SecurityException ex) {
    LOG.warn("Cannot access storage directory " + rootPath, ex);
    return StorageState.NON_EXISTENT;
  }

  this.lock(); // lock storage if it exists

  if (startOpt == HdfsServerConstants.StartupOption.FORMAT)
    return StorageState.NOT_FORMATTED;

  if (startOpt != HdfsServerConstants.StartupOption.IMPORT) {
    storage.checkOldLayoutStorage(this);
  }

  // check whether current directory is valid
  File versionFile = getVersionFile();
  boolean hasCurrent = versionFile.exists();

  // check which directories exist
  boolean hasPrevious = getPreviousDir().exists();
  boolean hasPreviousTmp = getPreviousTmp().exists();
  boolean hasRemovedTmp = getRemovedTmp().exists();
  boolean hasFinalizedTmp = getFinalizedTmp().exists();
  boolean hasCheckpointTmp = getLastCheckpointTmp().exists();

  if (!(hasPreviousTmp || hasRemovedTmp
      || hasFinalizedTmp || hasCheckpointTmp)) {
    // no temp dirs - no recovery
    if (hasCurrent)
      return StorageState.NORMAL;
    if (hasPrevious)
      throw new InconsistentFSStateException(root,
                          "version file in current directory is missing.");
    return StorageState.NOT_FORMATTED;
  }

  if ((hasPreviousTmp?1:0) + (hasRemovedTmp?1:0)
      + (hasFinalizedTmp?1:0) + (hasCheckpointTmp?1:0) > 1)
    // more than one temp dirs
    throw new InconsistentFSStateException(root,
                                           "too many temporary directories.");

  // # of temp dirs == 1 should either recover or complete a transition
  if (hasCheckpointTmp) {
    return hasCurrent ? StorageState.COMPLETE_CHECKPOINT
                      : StorageState.RECOVER_CHECKPOINT;
  }

  if (hasFinalizedTmp) {
    if (hasPrevious)
      throw new InconsistentFSStateException(root,
                                             STORAGE_DIR_PREVIOUS + " and " + STORAGE_TMP_FINALIZED
                                             + "cannot exist together.");
    return StorageState.COMPLETE_FINALIZE;
  }

  if (hasPreviousTmp) {
    if (hasPrevious)
      throw new InconsistentFSStateException(root,
                                             STORAGE_DIR_PREVIOUS + " and " + STORAGE_TMP_PREVIOUS
                                             + " cannot exist together.");
    if (hasCurrent)
      return StorageState.COMPLETE_UPGRADE;
    return StorageState.RECOVER_UPGRADE;
  }

  assert hasRemovedTmp : "hasRemovedTmp must be true";
  if (!(hasCurrent ^ hasPrevious))
    throw new InconsistentFSStateException(root,
                                           "one and only one directory " + STORAGE_DIR_CURRENT 
                                           + " or " + STORAGE_DIR_PREVIOUS 
                                           + " must be present when " + STORAGE_TMP_REMOVED
                                           + " exists.");
  if (hasCurrent)
    return StorageState.COMPLETE_ROLLBACK;
  return StorageState.RECOVER_ROLLBACK;
}