Failed to add new DataNode in pipeline and will be resulted into write failure.
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Key: HDFS-3091
URL: https://issues.apache.org/jira/browse/HDFS-3091
Project: Hadoop HDFS
Issue Type: Bug
Components: data-node, hdfs client, name-node
Affects Versions: 0.23.0, 0.24.0
Reporter: Uma Maheswara Rao G
When verifying the HDFS-1606 feature, Observed couple of issues.
Presently the ReplaceDatanodeOnFailure policy satisfies even though we dont
have enough DN to replcae in cluster and will be resulted into write failure.
{quote}
12/03/13 14:27:12 WARN hdfs.DFSClient: DataStreamer Exception
java.io.IOException: Failed to add a datanode: nodes.length != original.length
+ 1, nodes=[10.18.52.55:50010], original=[10.18.52.55:50010]
at
org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.findNewDatanode(DFSOutputStream.java:778)
at
org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.addDatanode2ExistingPipeline(DFSOutputStream.java:834)
at
org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.setupPipelineForAppendOrRecovery(DFSOutputStream.java:930)
at
org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.processDatanodeError(DFSOutputStream.java:741)
at
org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:416)
{quote}
Lets take some cases:
1) Replication factor 3 and cluster size also 3 and unportunately pipeline
drops to 1.
ReplaceDatanodeOnFailure will be satisfied because existings(1)<= replication/2
(3/2==1).
But when it finding the new node to replace obiously it can not find the new
node and the sanity check will fail.
This will be resulted to Wite failure.
2) Replication factor 10 (accidentally user sets the replication factor to
higher value than cluster size),
Cluser has only 5 datanodes.
Here even if one node fails also write will fail with same reason.
Because pipeline max will be 5 and killed one datanode, then existings will
be 4
existings(4)<= replication/2(10/2==5) will be satisfied and obiously it can
not replace with the new node as there is no extra nodes exist in the cluster.
This will be resulted to write failure.
3) sync realted opreations also fails in this situations ( will post the clear
scenarios)
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