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From "Rakesh R (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7116) Add a command to get the bandwidth of balancer
Date Wed, 20 May 2015 18:00:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14552774#comment-14552774

Rakesh R commented on HDFS-7116:

Hi [~ajisakaa], its really an interesting feature and would like to take this ahead. To begin
with, I have gone through the {{-setBalancerBandwidth}} feature. Here, Namenode is sending
the {{DNA_BALANCERBANDWIDTHUPDATE}} command to the Datanodes as a heartbeat response and Datanode
will update the new bandwidth value. In normal case, after setting the bandwidth all the datanodes
will have the same value. But I could see few corner cases where all the Datanodes in a cluster
not having unique bandwidth value.

Case-1) Newly added Datanodes will not aware about the new value and will have the default
bandwidth value. 
Case-2) Assume we have 10 Datanodes, after sending heartbeat responses to 1 to 5 Datanodes,
unfortunately Namenode restarted. Since bandwidth value is not persisted restarted Namenode
will not have the new bandwidth value. Now, the rest of the 6 to 10 Datanodes will be having
old value.

Is this expected behavior?. If yes, we have to design the {{-getBalancerBandwidth}} command
in such a way to list each Datanode with the corresponding bandwidth value like, {{each Datanode
= bandwidth value}}. Any thoughts?

> Add a command to get the bandwidth of balancer
> ----------------------------------------------
>                 Key: HDFS-7116
>                 URL: https://issues.apache.org/jira/browse/HDFS-7116
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: balancer & mover
>            Reporter: Akira AJISAKA
> Now reading logs is the only way to check how the balancer bandwidth is set. It would
be useful for administrators if they can get the parameter via CLI.

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