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From "Stephen O'Donnell (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-14333) Datanode fails to start if any disk has errors during Namenode registration
Date Mon, 04 Mar 2019 17:18:00 GMT
Stephen O'Donnell created HDFS-14333:
----------------------------------------

             Summary: 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


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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