HDFS-16985. delete local block file when FileNotFoundException occurred may lead to missing block.

Author: wangchengwei

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

@@ -351,11 +351,16 @@ class BlockSender implements java.io.Closeable {
         } catch (FileNotFoundException e) {
           if ((e.getMessage() != null) && !(e.getMessage()
               .contains("Too many open files"))) {
-            // The replica is on its volume map but not on disk
+            // The replica seems is on its volume map but not on disk.
+            // We can't confirm here is block file lost or disk failed.
+            // If block lost:
+            //    deleted local block file is completely unnecessary
+            // If disk failed:
+            //    deleted local block file here may lead to missing-block
+            //    when it with only 1 replication left now.
+            // So just notify namenode is ok.
             datanode
                 .notifyNamenodeDeletedBlock(block, replica.getStorageUuid());
-            datanode.data.invalidate(block.getBlockPoolId(),
-                new Block[] {block.getLocalBlock()});
           }
           throw e;
         } finally {