HDFS-11547. Add logs for slow BlockReceiver while writing data to disk. Contributed by Xiaobing Zhou.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockReceiver.java

@@ -711,6 +711,10 @@ private int receivePacket() throws IOException {
           streams.writeDataToDisk(dataBuf.array(),
               startByteToDisk, numBytesToDisk);
           long duration = Time.monotonicNow() - begin;
+          if (duration > datanodeSlowLogThresholdMs) {
+            LOG.warn("Slow BlockReceiver write data to disk cost:" + duration
+                + "ms (threshold=" + datanodeSlowLogThresholdMs + "ms)");
+          }
 
           if (duration > maxWriteToDiskMs) {
             maxWriteToDiskMs = duration;