apache/hadoop · error · IOException

Failed to create ${realPmemDir}

Error message

Failed to create ${realPmemDir}

What it means

Error "Failed to create ${realPmemDir}" thrown in apache/hadoop.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/PmemVolumeManager.java:332

  public void recoverBlockKeyToVolume(ExtendedBlockId key, byte volumeIndex) {
    blockKeyToVolume.put(key, volumeIndex);
  }

  @VisibleForTesting
  static File verifyIfValidPmemVolume(File pmemDir)
      throws IOException {
    if (!pmemDir.exists()) {
      final String message = pmemDir + " does not exist";
      throw new IOException(message);
    }
    if (!pmemDir.isDirectory()) {
      final String message = pmemDir + " is not a directory";
      throw new IllegalArgumentException(message);
    }

    File realPmemDir = new File(getRealPmemDir(pmemDir.getPath()));
    if (!realPmemDir.exists() && !realPmemDir.mkdir()) {
      throw new IOException("Failed to create " + realPmemDir.getPath());
    }

    String uuidStr = UUID.randomUUID().toString();
    String testFilePath = realPmemDir.getPath() + "/.verify.pmem." + uuidStr;
    byte[] contents = uuidStr.getBytes(StandardCharsets.UTF_8);
    RandomAccessFile testFile = null;
    MappedByteBuffer out = null;
    try {
      testFile = new RandomAccessFile(testFilePath, "rw");
      out = testFile.getChannel().map(FileChannel.MapMode.READ_WRITE, 0,
          contents.length);
      if (out == null) {
        throw new IOException(
            "Failed to map the test file under " + realPmemDir);
      }
      out.put(contents);
      // Forces to write data to storage device containing the mapped file
      out.force();

View on GitHub (pinned to 2add963021)

Solutions

1. Check permissions and free space on the pmem device so the DataNode can create the working directory.
2. Verify the pmem device is mounted read-write and healthy.

When it happens

Trigger: Pmem cache initialization when the real pmem directory cannot be created, usually a permissions or mount problem.

Common situations: See trigger scenarios.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/2307b8108ab61ad8. Report an issue: GitHub.