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https://issues.apache.org/jira/browse/HDFS-10967?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Zhe Zhang updated HDFS-10967:
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Attachment: HDFS-10967.00.patch
Thought more about the design options. Currently I think the most reasonable
direction is to:
# Apply the logic only when trying to {{chooseRemoteRack}} -- that is when the
2nd and 3rd replicas are being placed. In most cases, triaging the 2nd and 3rd
replicas from near-full DNs is already sufficient to address the balancing
issue.
# Use the percentage of remaining capacity because current NN metrics are
already based on percentage. So admins should be most comfortable operating
based on it (e.g. {{97%}} full).
# Do random selection a few times instead of completely avoiding near-full DNs.
Like mentioned above, imbalance will cause an issue only if a large number of
DNs are near full. So a statistical solution should be sufficient.
> Add configuration for BlockPlacementPolicy to avoid near-full DataNodes
> -----------------------------------------------------------------------
>
> Key: HDFS-10967
> URL: https://issues.apache.org/jira/browse/HDFS-10967
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Reporter: Zhe Zhang
> Assignee: Zhe Zhang
> Labels: balancer
> Attachments: HDFS-10967.00.patch, HDFS-10967.poc.patch
>
>
> Large production clusters are likely to have heterogeneous nodes in terms of
> storage capacity, memory, and CPU cores. It is not always possible to
> proportionally ingest data into DataNodes based on their remaining storage
> capacity. Therefore it's possible for a subset of DataNodes to be much closer
> to full capacity than the rest.
> This heterogeneity is most likely rack-by-rack -- i.e. _m_ whole racks of
> low-storage nodes and _n_ whole racks of high-storage nodes. So It'd be very
> useful if we can lower the chance for those near-full DataNodes to become
> destinations for the 2nd and 3rd replicas.
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