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https://issues.apache.org/jira/browse/HADOOP-1652?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hairong Kuang updated HADOOP-1652:
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Attachment: RebalanceDesign5.pdf
Attached is a new version of the design document which includes the following
changes:
1. A block is pulled by a destination instead of pushed from a source.
2. A block can be pulled from a proxy source which contains the block and is
closer to the destination or less loaded than the source.
3. A source does not delete a block by itself. Instead a destination notifies
the name node that a block is copied and a hint that a replica at the source
should be removed if the block is over replicated. When the name node decides
to remove an excessive replica, it favors the hint as long as doing so does not
violate the rebalancing requirement 1. A source removes the block upon a
request from the name node.
> Rebalance data blocks when new data nodes added or data nodes become full
> -------------------------------------------------------------------------
>
> Key: HADOOP-1652
> URL: https://issues.apache.org/jira/browse/HADOOP-1652
> Project: Hadoop
> Issue Type: New Feature
> Components: dfs
> Affects Versions: 0.13.0
> Reporter: Hairong Kuang
> Assignee: Hairong Kuang
> Fix For: 0.15.0
>
> Attachments: RebalanceDesign4.pdf, RebalanceDesign5.pdf
>
>
> When a new data node joins hdfs cluster, it does not hold much data. So any
> map task assigned to the machine most likely does not read local data, thus
> increasing the use of network bandwidth. On the other hand, when some data
> nodes become full, new data blocks are placed on only non-full data nodes,
> thus reducing their read parallelism.
> This jira aims to find an approach to redistribute data blocks when imbalance
> occurs in the cluster. An solution should meet the following requirements:
> 1. It maintains data availablility guranteens in the sense that rebalancing
> does not reduce the number of replicas that a block has or the number of
> racks that the block resides.
> 2. An adminstrator should be able to invoke and interrupt rebalancing from a
> command line.
> 3. Rebalancing should be throttled so that rebalancing does not cause a
> namenode to be too busy to serve any incoming request or saturate the network.
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