caozhiqiang created HDFS-16456:
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Summary: EC: Decommission a rack with only on dn will fail when
the rack number is equal with replication
Key: HDFS-16456
URL: https://issues.apache.org/jira/browse/HDFS-16456
Project: Hadoop HDFS
Issue Type: Bug
Components: ec, namenode
Affects Versions: 3.1.1
Reporter: caozhiqiang
In below scenario, decommission will fail by TOO_MANY_NODES_ON_RACK reason:
# Enable EC policy, such as RS-6-3-1024k.
# The rack number in this cluster is equal with the replication number(9)
# A rack only has one DN, and decommission this DN.
The root cause is in
BlockPlacementPolicyRackFaultTolerant::getMaxNodesPerRack() function, it will
give a limit parameter maxNodesPerRack for choose targets. In this scenario,
the maxNodesPerRack is 1, which means each rack can only be chosen one datanode.
When we decommission one dn which is only one node in its rack, the
chooseOnce() in BlockPlacementPolicyRackFaultTolerant::chooseTargetInOrder()
will throw NotEnoughReplicasException, but the exception will not be caught and
fail to fallback to chooseEvenlyFromRemainingRacks() function.
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