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https://issues.apache.org/jira/browse/HDFS-7866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15186270#comment-15186270
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Jing Zhao commented on HDFS-7866:
---------------------------------

Sorry for the confusion. I mean the change on {{ErasureCodingPolicyProto}} only 
affects RPC calls. It will break the wire compatibility between new client and 
old NN, as you mentioned. This is the scenario we have in rolling upgrade or 
different versions are mixed in the same cluster. Because EC is only in 3.0, we 
can ask existing EC users to upgrade to the new version, and not to allow new 
clients and old NN coexisting in the cluster.

> Erasure coding: NameNode manages multiple erasure coding policies
> -----------------------------------------------------------------
>
>                 Key: HDFS-7866
>                 URL: https://issues.apache.org/jira/browse/HDFS-7866
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Kai Zheng
>            Assignee: Rui Li
>         Attachments: HDFS-7866-v1.patch, HDFS-7866-v2.patch, 
> HDFS-7866-v3.patch, HDFS-7866.10.patch, HDFS-7866.11.patch, 
> HDFS-7866.12.patch, HDFS-7866.13.patch, HDFS-7866.4.patch, HDFS-7866.5.patch, 
> HDFS-7866.6.patch, HDFS-7866.7.patch, HDFS-7866.8.patch, HDFS-7866.9.patch
>
>
> This is to extend NameNode to load, list and sync predefine EC schemas in 
> authorized and controlled approach. The provided facilities will be used to 
> implement DFSAdmin commands so admin can list available EC schemas, then 
> could choose some of them for target EC zones.



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