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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7859) Erasure Coding: Persist EC schemas in NameNode
Date Tue, 14 Apr 2015 21:33:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14494933#comment-14494933
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Tsz Wo Nicholas Sze commented on HDFS-7859:
-------------------------------------------

I have the following questions:
- How to add a schema?  Using a command?
- Then, is it possible to delete a schema?  It seems that we have to support deletion since
a schema may be created by mistake or there could be typos when creating a schema.
- If deletion is supported, what to do with the existing files with that schema?
- Do we support renaming schema?
- Does a EC schema have a schema ID?

I think we need a design for EC schema to answer all these questions and specify what operations
are supported.

BTW, we only support one schema (6,3)-Reed-Solomon in the first phase HDFS-7285.  I think
we should focus on finishing a complete, working basic EC feature and get HDFS-7285 merged
to trunk.  How about moving this JIRA and related JIRAs to HDFS-8031 and defer the work? 
Sorry for commenting on this late and thanks for all the good works.

> 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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