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https://issues.apache.org/jira/browse/HADOOP-2559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12571334#action_12571334
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lohit vijayarenu commented on HADOOP-2559:
------------------------------------------
I ran random writer and sort benchmark on trunk, trunk+patch1 (allocates 3rd
block on same rack as 2nd block is located) and trunk+patch2 (which includes
patch1 and also allocates first block on local rack, instead of local node).
The tests were run on 100 nodes. I ran 2 randomwriters back to back and 2 sorts
back to back on the data generated by random writers.
Here are the results
{noformat}
Job TRUNK TRUNK+Path1 TRUNK+Patch2
RandomWriter 500 563 689
RandomWriter 495 486 625
Sort 1563 1737
1614
Sort 1680 1675
1678
{noformat}
> DFS should place one replica per rack
> -------------------------------------
>
> Key: HADOOP-2559
> URL: https://issues.apache.org/jira/browse/HADOOP-2559
> Project: Hadoop Core
> Issue Type: Improvement
> Components: dfs
> Reporter: Runping Qi
> Assignee: lohit vijayarenu
> Attachments: HADOOP-2559-1.patch, HADOOP-2559-2.patch
>
>
> Currently, when writing out a block, dfs will place one copy to a local data
> node, one copy to a rack local node
> and another one to a remote node. This leads to a number of undesired
> properties:
> 1. The block will be rack-local to two tacks instead of three, reducing the
> advantage of rack locality based scheduling by 1/3.
> 2. The Blocks of a file (especiallya large file) are unevenly distributed
> over the nodes: One third will be on the local node, and two thirds on the
> nodes on the same rack. This may make some nodes full much faster than
> others,
> increasing the need of rebalancing. Furthermore, this also make some nodes
> become "hot spots" if those big
> files are popular and accessed by many applications.
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