Error "Failed to place enough replicas" Is Reported When HDFS Reads or Writes Files

Symptom

When a user performs a write operation on HDFS, the message "Failed to place enough replicas:expected…" is displayed.

Cause Analysis

• The data receiver of the DataNode is unavailable.

  The DataNode log is as follows:

  2016-03-17 18:51:44,721 | WARN | org.apache.hadoop.hdfs.server.datanode.DataXceiverServer@5386659f | hadoopc1h2:25009:DataXceiverServer: | DataXceiverServer.java:158
  java.io.IOException: Xceiver count 4097 exceeds the limit of concurrent xcievers: 4096
  at org.apache.hadoop.hdfs.server.datanode.DataXceiverServer.run(DataXceiverServer.java:140)
  at java.lang.Thread.run(Thread.java:745) 

• The disk space configured for the DataNode is insufficient.
• DataNode heartbeats are delayed.

Solution

• If the DataNode data receiver is unavailable, add the value of the HDFS parameter dfs.datanode.max.transfer.threads on Manager.
• If disk space or CPU resources are insufficient, add DataNodes or ensure that disk space and CPU resources are available.
• If the network is faulty, ensure that the network is available.