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https://issues.apache.org/jira/browse/HDFS-9923?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15292228#comment-15292228
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Wei-Chiu Chuang commented on HDFS-9923:
---------------------------------------
HADOOP-12973 unintentionally changed this behavior: du errors will be caught
and logged, but not propagated to the caller.
> Datanode disk failure handling is not consistent
> ------------------------------------------------
>
> Key: HDFS-9923
> URL: https://issues.apache.org/jira/browse/HDFS-9923
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Wei-Chiu Chuang
> Labels: failure-handling, supportability
>
> Disk failures are hard to handle. This JIRA is created to discuss/improve
> disk failure handling in a better/consistent manner.
> For one thing, disks can fail in multiple different ways: the hardware might
> be failing, disk space is full, checksum error ... For others, hardware
> abstracts out the details, so it's hard for software to handle them.
> There are currently three disk check mechanisms in HDFS, as far as I know:
> {{BlockScanner}}, {{BlockPoolSlice#checkDirs}} and {{DU}}. Disk errors are
> handled differently.
> This JIRA is more focused on {{DU}} error handling. {{DU}} may emit errors
> like this:
> {noformat}
> 2016-02-18 02:23:36,224 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Caught
> exception while scanning /data/8/dfs/dn/current.
> Will throw later.
> ExitCodeException exitCode=1: du: cannot access
> `/data/8/dfs/dn/current/BP-1018136951-49.4.167.110-1403564146510/current/finalized/subdir228/subdir11/blk_
> 1088686909': Input/output error
> du: cannot access
> `/data/8/dfs/dn/current/BP-1018136951-49.4.167.110-1403564146510/current/finalized/subdir228/subdir11/blk_1088686909_14954023.meta':
> Inp
> ut/output error
> {noformat}
> I found {{DU}} errors are not handled consistently while working on HDFS-9908
> (Datanode should tolerate disk scan failure during NN handshake), and it all
> depends on who catches the exception.
> For example,
> * if DU returns error during NN handshake, DN will not be able to join the
> cluster at all(HDFS-9908);
> * however, if the same exception is caught in {{BlockPoolSlice#saveDfsUsed}},
> data node will only log a warning and do nothing (HDFS-5498).
> * in some cases, the exception handler invokes {{BlockPoolSlice#checkDirs}},
> but since it only checks three directories, it is very unlikely to find the
> files that have the error. {{BlockReceiver#(constructor)}}
> So my ask is: should the error be handled in a consistent manner? Should data
> node report to the name nodes about the disk failures (this is the
> BlockScanner approach), and should data node takes this volume offline
> automatically if DU returns an error? (this is the {{checkDirs}} approach)
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