Mark Ormesher created HDFS-15103:
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             Summary: JMX endpoint and "dfsadmin" report 1 corrupt block; 
"fsck" reports 0
                 Key: HDFS-15103
                 URL: https://issues.apache.org/jira/browse/HDFS-15103
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: namenode
    Affects Versions: 3.2.1
         Environment: * CentOS 7
 * HDFS 3.2.1
 * 2x HA NNs
 * 5x identical DNs
            Reporter: Mark Ormesher


We're seeing a long-running discrepancy between the number of corrupted blocks 
reported by the JMX endpoint and {{dfsadmin -report}} (1) and by {{fsck /}} 
(0). This has persisted through rolling restarts of the NNs and DNs, and 
through complete shutdowns for the HDFS cluster for unrelated maintenance.

{panel:title=JMX endpoint snippet}
{code}
(...)
    "CorruptBlocks" : 1,
    "ScheduledReplicationBlocks" : 0,
    "PendingDeletionBlocks" : 0,
    "LowRedundancyReplicatedBlocks" : 0,
    "CorruptReplicatedBlocks" : 1,
    "MissingReplicatedBlocks" : 0,
    "MissingReplicationOneBlocks" : 0,
(...)
{code}
{panel}

{panel:title=dfsadmin -report}
{code}
$ ./hdfs dfsadmin -report | grep -i corrupt
  Blocks with corrupt replicas: 1
  Block groups with corrupt internal blocks: 0
{code}
{panel}

{panel:title=fsck /}
{code}
$ ./hdfs fsck / -files -blocks | grep -i corrupt
  Corrupt blocks:                0
  Corrupt block groups:          0
{code}
{panel}

I've read through the related tickets below, all of which suggest this issue 
was resolved in 2.7.8, but we're seeing it in 3.2.1.

https://issues.apache.org/jira/browse/HDFS-8533
https://issues.apache.org/jira/browse/HDFS-10213
https://issues.apache.org/jira/browse/HDFS-13999

How can we work out whether we really do have a corrupt block, and if we do how 
can we work out which block it is if {{fsck}} thinks everything is fine?



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