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From "Wei-Chiu Chuang (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-10777) DataNode should report&remove volume failures if DU cannot access files
Date Thu, 18 Aug 2016 20:49:21 GMT
Wei-Chiu Chuang created HDFS-10777:
--------------------------------------

             Summary: DataNode should report&remove volume failures if DU cannot access
files
                 Key: HDFS-10777
                 URL: https://issues.apache.org/jira/browse/HDFS-10777
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: datanode
    Affects Versions: 2.8.0
            Reporter: Wei-Chiu Chuang
            Assignee: Wei-Chiu Chuang


HADOOP-12973 refactored DU and makes it pluggable. The refactory has a side-effect that if
DU encounters an exception, the exception is caught, logged and ignored, essentially fixes
HDFS-9908 (in which case runaway exceptions prevent DataNodes from handshaking with NameNodes).

However, this "fix" is not good, in the sense that if the disk is bad, there is no immediate
action made by the DataNode other than logging the exception. Existing {{FsDatasetSpi#checkDataDir}}
has been reduced to only check a few number of directories blindly. If a disk goes bad, it
is often possible that only a few files are bad initially and that by checking only a small
number of directories it is easy to overlook the degraded disk.

I propose: in addition to logging the exception, DataNode should proactively verify the files
are not accessible, remove the volume, and make the failure visible by showing it in JMX,
so that administrators can spot the failure via monitoring systems.

A different fix, based on HDFS-9908, is needed before Hadoop 2.8.0



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