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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1652) Rebalance data blocks when new data nodes added or data nodes become full
Date Fri, 10 Aug 2007 22:57:42 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1652?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Hairong Kuang updated HADOOP-1652:

    Attachment: RebalanceDesign4.pdf

This is a more detailed design document for the rebalancing tool. A major change is that the
rebalancing decisions are made in a seperate process from name node. Data nodes are throttled
to prevent rebalancing using too much network bandwidth. I also add the protocol design, race
condition discusssion, and a test plan.

> 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
> 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
> 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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