0.23: Changes to balancer bandwidth should not require datanode restart.
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Key: HDFS-2202
URL: https://issues.apache.org/jira/browse/HDFS-2202
Project: Hadoop HDFS
Issue Type: Bug
Components: balancer, data-node
Affects Versions: 0.20.205.0
Reporter: Eric Payne
Assignee: Eric Payne
Fix For: 0.20.205.0
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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