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From "Stephen O'Donnell (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HDFS-14333) Datanode fails to start if any disk has errors during Namenode registration
Date Mon, 04 Mar 2019 17:50:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-14333?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16783596#comment-16783596
] 

Stephen O'Donnell edited comment on HDFS-14333 at 3/4/19 5:49 PM:
------------------------------------------------------------------

I have added a v1 patch which currently has no tests included.

The IO exception at runtime would generally come from BlockPoolSlice$AddReplicaProcessor.compute(),
but there are no obvious fault injectors I can see.

Would it make sense to introduce a 'simulate failure' flag to that code to test this, or is
there a better way? I would be happy to hear suggestions on this.

I have added the exception handing to FsVolumeList.getAllVolumesMap, but it probably makes
sense to add the same logic to FsVolumeList.addBlockPool() too. Even though du errors cannot
reach that code now, it would be a good safety net in case the du logic changes or other errors
slip through. A test for this may be harder, as this is a 'should not happen' scenario in
the current code.


was (Author: sodonnell):
I have added a v1 patch which currently has no tests included.

The IO exception at runtime would generally come from BlockPoolSlice$AddReplicaProcessor.compute(),
but there are no obvious fault injectors I can see.

Would it make sense to introduce a 'simulate failure' flag to that code to test this, or is
there a better way? I would be happy to hear suggestions on this.

I have added the exception handing to getAllVolumesMap, but it probably makes sense to add
the same logic to FsVolumeList.addBlockPool() too. Even though du errors cannot reach that
code now, it would be a good safety net in case the du logic changes or other errors slip
through.

> Datanode fails to start if any disk has errors during Namenode registration
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-14333
>                 URL: https://issues.apache.org/jira/browse/HDFS-14333
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>    Affects Versions: 3.3.0
>            Reporter: Stephen O'Donnell
>            Assignee: Stephen O'Donnell
>            Priority: Major
>         Attachments: HDFS-14333.001.patch
>
>
> This is closely related to HDFS-9908, where it was reported that a datanode would fail
to start if an IO error occurred on a single disk when running du during Datanode registration.
That Jira was closed due to HADOOP-12973 which refactored how du is called and prevents any
exception being thrown. However this problem can still occur if the volume has errors (eg
permission or filesystem corruption) when the disk is scanned to load all the replicas. The
method chain is:
> DataNode.initBlockPool -> FSDataSetImpl.addBlockPool -> FSVolumeList.getAllVolumesMap
-> Throws exception which goes unhandled.
> The DN logs will contain a stack trace for the problem volume, so the workaround is to
remove the volume from the DN config and the DN will start, but the logs are a little confusing,
so its always not obvious what the issue is.
> These are the cut down logs from an occurrence of this issue.
> {code}
> 2019-03-01 08:58:24,830 INFO org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl:
Scanning block pool BP-240961797-x.x.x.x-1392827522027 on volume /data/18/dfs/dn/current...
> ...
> 2019-03-01 08:58:27,029 WARN org.apache.hadoop.fs.CachingGetSpaceUsed: Could not get
disk usage information
> ExitCodeException exitCode=1: du: cannot read directory `/data/18/dfs/dn/current/BP-240961797-x.x.x.x-1392827522027/current/finalized/subdir149/subdir215':
Permission denied
> du: cannot read directory `/data/18/dfs/dn/current/BP-240961797-x.x.x.x-1392827522027/current/finalized/subdir149/subdir213':
Permission denied
> du: cannot read directory `/data/18/dfs/dn/current/BP-240961797-x.x.x.x-1392827522027/current/finalized/subdir97/subdir25':
Permission denied
> 	at org.apache.hadoop.util.Shell.runCommand(Shell.java:601)
> 	at org.apache.hadoop.util.Shell.run(Shell.java:504)
> 	at org.apache.hadoop.fs.DU$DUShell.startRefresh(DU.java:61)
> 	at org.apache.hadoop.fs.DU.refresh(DU.java:53)
> 	at org.apache.hadoop.fs.CachingGetSpaceUsed.init(CachingGetSpaceUsed.java:84)
> 	at org.apache.hadoop.fs.GetSpaceUsed$Builder.build(GetSpaceUsed.java:166)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.<init>(BlockPoolSlice.java:145)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.addBlockPool(FsVolumeImpl.java:881)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeList$2.run(FsVolumeList.java:412)
> ...
> 2019-03-01 08:58:27,043 INFO org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl:
Time taken to scan block pool BP-240961797-x.x.x.x-1392827522027 on /data/18/dfs/dn/current:
2202ms
> {code}
> So we can see a du error occurred, was logged but not re-thrown (due to HADOOP-12973)
and the blockpool scan completed. However then in the 'add replicas to map' logic, we got
another exception stemming from the same problem:
> {code}
> 2019-03-01 08:58:27,564 INFO org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl:
Adding replicas to map for block pool BP-240961797-x.x.x.x-1392827522027 on volume /data/18/dfs/dn/current...
> ...
> 2019-03-01 08:58:31,155 INFO org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl:
Caught exception while adding replicas from /data/18/dfs/dn/current. Will throw later.
> java.io.IOException: Invalid directory or I/O error occurred for dir: /data/18/dfs/dn/current/BP-240961797-x.x.x.x-1392827522027/current/finalized/subdir149/subdir215
> 	at org.apache.hadoop.fs.FileUtil.listFiles(FileUtil.java:1167)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.addToReplicasMap(BlockPoolSlice.java:445)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.addToReplicasMap(BlockPoolSlice.java:448)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.addToReplicasMap(BlockPoolSlice.java:448)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.getVolumeMap(BlockPoolSlice.java:342)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.getVolumeMap(FsVolumeImpl.java:861)
> 	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeList$1.run(FsVolumeList.java:191)
> < The message 2019-03-01 08:59:00,989 INFO org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl:
Time to add replicas to map for block pool BP-240961797-x.x.x.x-1392827522027 on volume xxx
did not appear for this volume as it failed >
> {code}
> The exception is re-thrown, so the DN fails registration and then retries. Then it finds
all volumes already locked and exits with a 'all volumes failed' error.
> I believe we should handle the failing volume like a runtime volume failure and only
abort the DN if too many volumes have failed.
> I will post a patch for this.



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