[
https://issues.apache.org/jira/browse/HDFS-7891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14380038#comment-14380038
]
Walter Su commented on HDFS-7891:
---------------------------------
Thanks Tsz for analysis so deeply. This is a great thought about how we can
optimize the policy. But I think place 2 replica under same rack doesn't reduce
traffic.
Why the default policy place 1st replica in local rack. And 2nd and 3rd in
the same remote rack? Why 3rd in the same rack with 2nd. Because the pipeline
mechanism allows 3rd replica comes from 2nd. And also because the content is
the same. Because three replica is the same block. 3rd replica is not from
client.
Come back to this jira and EC group. I think when we use stripe layout, even
when stripe layout is not used. All 6+3 replica(it's better called blocks
belonging to same group) comes from client. As long as the replica is place on
the remote rack, the traffic is the same.
Correct me if I was wrong.
> A block placement policy with best fault tolerance
> --------------------------------------------------
>
> Key: HDFS-7891
> URL: https://issues.apache.org/jira/browse/HDFS-7891
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Walter Su
> Assignee: Walter Su
> Attachments: HDFS-7891.002.patch, HDFS-7891.003.patch,
> HDFS-7891.004.patch, HDFS-7891.patch, PlacementPolicyBenchmark.txt,
> testresult.txt
>
>
> a block placement policy tries its best to place replicas to most racks.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
