Arpit Agarwal created HDFS-5412:
-----------------------------------

             Summary: Directory scanner fails to propagate volume information 
in disk report
                 Key: HDFS-5412
                 URL: https://issues.apache.org/jira/browse/HDFS-5412
             Project: Hadoop HDFS
          Issue Type: Sub-task
            Reporter: Arpit Agarwal
            Assignee: Arpit Agarwal


The directory scanner periodically compiles a report of differences between the 
datanode's on-disk and in-memory state to reconcile differences.

The code to generate the reports is in {{DirectoryScanner#scan}} and 
{{DirectoryScanner#getDiskReport}}. It looks like the volume field in 
{{ScanInfo}} is not correctly initialized while compiling the diffs. This was 
not an issue before but now we depend on the volume information being present. 
The bug triggers the following NPE during a scan if a block is present in the 
Datanode's in-memory block map but missing on disk:

{code}
java.lang.NullPointerException
        at 
org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.checkAndUpdate(FsDatasetImpl.java:1404)
        at 
org.apache.hadoop.hdfs.server.datanode.DirectoryScanner.reconcile(DirectoryScanner.java:416)
        at 
org.apache.hadoop.hdfs.server.datanode.DirectoryScanner.run(DirectoryScanner.java:365)
        at 
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:439)
        at 
java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:317)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:150)
        at 
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$101(ScheduledThreadPoolExecutor.java:98)
        at 
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.runPeriodic(ScheduledThreadPoolExecutor.java:180)
        at 
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:204)
        at 
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
        at 
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
        at java.lang.Thread.run(Thread.java:695)
{code}



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