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Posted to hdfs-dev@hadoop.apache.org by "Tsz Wo (Nicholas), SZE (JIRA)" <ji...@apache.org> on 2011/01/24 19:54:43 UTC
[jira] Created: (HDFS-1595) DFSClient may incorrectly detect
datanode failure
DFSClient may incorrectly detect datanode failure
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Key: HDFS-1595
URL: https://issues.apache.org/jira/browse/HDFS-1595
Project: Hadoop HDFS
Issue Type: Bug
Components: data-node, hdfs client
Affects Versions: 0.20.4
Reporter: Tsz Wo (Nicholas), SZE
Suppose a source datanode S is writing to a destination datanode D in a write pipeline. We have an implicit assumption that _if S catches an exception when it is writing to D, then D is faulty and S is fine._ As a result, DFSClient will take out D from the pipeline, reconstruct the write pipeline with the remaining datanodes and then continue writing .
However, we find a case that the faulty machine F is indeed S but not D. In the case we found, F has a faulty network interface (or a faulty switch port) in such a way that the faulty network interface works fine when sending out a small amount of data, say 1MB, but it fails when sending out a large amount of data, say 100MB.
It is even worst if F is the first datanode in the pipeline. Consider the following:
# DFSClient creates a pipeline with three datanodes. The first of the datanode is F.
# F catches an IOException when writing to the second datanode. Then, F reports the second datanode has error.
# DFSClient removes the second datanode from the pipeline and continue writing with the remaining datanode(s).
# The pipeline now has two datanodes but (2) and (3) repeat.
# Now, only F remains in the pipeline. DFSClient continues writing with one replica in F.
# The write succeeds and DFSClient is able to close the file successfully.
# The block is under replicated. The NameNode schedules replication from F to some other datanode D.
# The replication fails from the same reason. D reports to the NameNode that the replica in F is corrupted.
# The NameNode marks the replica in F is corrupted.
# The block is corrupted since no replica is available.
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