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From "Eric Payne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2171) Changes to balancer bandwidth should not require datanode restart.
Date Wed, 20 Jul 2011 15:34:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13068437#comment-13068437

Eric Payne commented on HDFS-2171:

Thanks Aaron and Todd.

If the solutions between and trunk turn out to be too different, I would like to
open a separate Jira for and trunk.

One problem with the Reconfigurable class is that it isn't defined in branches outside of

Even with the Reconfigurable implementation, wouldn't there still need to be some interface
defined (maybe via dfsadmin) that would trigger each datanode to reset that value? This seems
to be somewhat of a maintenance problem because if the request happens when a node is down,
that node won't have the new value.

> Changes to balancer bandwidth should not require datanode restart.
> ------------------------------------------------------------------
>                 Key: HDFS-2171
>                 URL: https://issues.apache.org/jira/browse/HDFS-2171
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: balancer, data-node
>    Affects Versions:
>            Reporter: Eric Payne
>            Assignee: Eric Payne
>             Fix For:
> Currently in order to change the value of the balancer bandwidth (dfs.datanode.balance.bandwidthPerSec),
the datanode daemon must be restarted.
> The optimal value of the bandwidthPerSec parameter is not always (almost never) known
at the time of cluster startup, but only once a new node is placed in the cluster and balancing
is begun. If the balancing is taking too long (bandwidthPerSec is too low) or the balancing
is taking up too much bandwidth (bandwidthPerSec is too high), the cluster must go into a
"maintenance window" where it is unusable while all of the datanodes are bounced. In large
clusters of thousands of nodes, this can be a real maintenance problem because these "mainenance
windows" can take a long time and there may have to be several of them while the bandwidthPerSec
is experimented with and tuned.
> A possible solution to this problem would be to add a -bandwidth parameter to the balancer
tool. If bandwidth is supplied, pass the value to the datanodes via the OP_REPLACE_BLOCK and
OP_COPY_BLOCK DataTransferProtocol requests. This would make it necessary, however, to change
the DataTransferProtocol version.

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