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https://issues.apache.org/jira/browse/HDFS-12151?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16090677#comment-16090677
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Sean Mackrory commented on HDFS-12151:
--------------------------------------
The problem is in lines added by HDFS-9807. When serving clients from before
that feature, no storage Ids will be provided, but we unconditionally address
the first element in the array. I was able to do a successful rolling upgrade
from HDFS 2 -> HDFS 3 by just checking the length first, and passing in null by
default.
> Hadoop 2 clients cannot writeBlock to Hadoop 3 DataNodes
> --------------------------------------------------------
>
> Key: HDFS-12151
> URL: https://issues.apache.org/jira/browse/HDFS-12151
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: rolling upgrades
> Reporter: Sean Mackrory
> Assignee: Sean Mackrory
>
> Trying to write to a Hadoop 3 DataNode with a Hadoop 2 client currently
> fails. On the client side it looks like this:
> {code}
> 17/07/14 13:31:58 INFO hdfs.DFSClient: Exception in
> createBlockOutputStream
> java.io.EOFException: Premature EOF: no length prefix available
> at
> org.apache.hadoop.hdfs.protocolPB.PBHelper.vintPrefixed(PBHelper.java:2280)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.createBlockOutputStream(DFSOutputStream.java:1318)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1237)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:449){code}
> But on the DataNode side there's an ArrayOutOfBoundsException because there
> aren't any targetStorageIds:
> {code}
> java.lang.ArrayIndexOutOfBoundsException: 0
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:815)
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:173)
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:107)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:290)
> at java.lang.Thread.run(Thread.java:745){code}
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