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https://issues.apache.org/jira/browse/HDFS-2554?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13437071#comment-13437071
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Andy Isaacson commented on HDFS-2554:
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bq. Also, I'm slightly altering your definition of "n" here, ie I'm considering
it "live" replicas, which doesn't include a decommissioning replica which you
might be considering "good" since it's a valid replica.
This is a good point. I'm tentatively going to agree with you, n is the number
of live replicas excluding decommissioning replicas.
This means that if all replicas of a block are on DNs which get decommissioned,
the block will temporarily be counted in MissingBlocks (either R1 or RN
depending on the value of r) until the block gets replicated to a live DN.
This is somewhat unfortunate since we don't actually lose the block at any
point in this process. Perhaps there's a need for an additional metric, but
I'm going to defer that until later.
> Add separate metrics for missing blocks with desired replication level 1
> ------------------------------------------------------------------------
>
> Key: HDFS-2554
> URL: https://issues.apache.org/jira/browse/HDFS-2554
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Affects Versions: 2.0.0-alpha
> Reporter: Todd Lipcon
> Assignee: Andy Isaacson
> Priority: Minor
>
> Some users use replication level set to 1 for datasets which are unimportant
> and can be lost with no worry (eg the output of terasort tests). But other
> data on the cluster is important and should not be lost. It would be useful
> to separate the metric for missing blocks by the desired replication level of
> those blocks, so that one could ignore missing blocks at repl 1 while still
> alerting on missing blocks with higher desired replication.
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