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https://issues.apache.org/jira/browse/HDFS-7859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14495498#comment-14495498
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Tsz Wo Nicholas Sze commented on HDFS-7859:
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> The patch under this JIRA handles saving / loading these default schemas in
> fsimage. I think this is necessary even without loading custom schemas from
> XML. Otherwise we cannot guarantee the NameNode which loads the fsimage has
> the same default schemas as the NameNode which saved it. It is obviously even
> more necessary when we add custom schemas ...
I think we should not persist anything to NN before we have a clear design
since we don't know what to persist. For example, should we persist schema ID?
We are not able to answer this question since we don't even know if a schema
should have an ID.
If we change the layout later on, it requires cluster upgrade for the new
layout and we have to support the old layout for backward compatibility.
For now, I suggest to just hard code the only (6,3)-Reed-Solomon schema. We
don't even need the xml file.
> Erasure Coding: Persist EC schemas in NameNode
> ----------------------------------------------
>
> Key: HDFS-7859
> URL: https://issues.apache.org/jira/browse/HDFS-7859
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Kai Zheng
> Assignee: Xinwei Qin
> Attachments: HDFS-7859.001.patch
>
>
> In meetup discussion with [~zhz] and [~jingzhao], it's suggested that we
> persist EC schemas in NameNode centrally and reliably, so that EC zones can
> reference them by name efficiently.
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