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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8833) Erasure coding: store EC schema and cell size in INodeFile and eliminate notion of EC zones
Date Wed, 05 Aug 2015 23:23:05 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14659173#comment-14659173
] 

Andrew Wang commented on HDFS-8833:
-----------------------------------

bq. My point is we should only use xattr for representing ec policy for file/dir, instead
of occupying several bits in INodeFile first then coming to xattr later.

I guess this is the core of the issue, since I don't understand your objection to using file
header bits. Are you worried that we will want to use these bits for another purpose? Or that
the code to later use an xattr will be complex? Would like to discuss this since it seems
like the focal point and influences our implementation choices.

> Erasure coding: store EC schema and cell size in INodeFile and eliminate notion of EC
zones
> -------------------------------------------------------------------------------------------
>
>                 Key: HDFS-8833
>                 URL: https://issues.apache.org/jira/browse/HDFS-8833
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>    Affects Versions: HDFS-7285
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>
> We have [discussed | https://issues.apache.org/jira/browse/HDFS-7285?focusedCommentId=14357754&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14357754]
storing EC schema with files instead of EC zones and recently revisited the discussion under
HDFS-8059.
> As a recap, the _zone_ concept has severe limitations including renaming and nested configuration.
Those limitations are valid in encryption for security reasons and it doesn't make sense to
carry them over in EC.
> This JIRA aims to store EC schema and cell size on {{INodeFile}} level. For simplicity,
we should first implement it as an xattr and consider memory optimizations (such as moving
it to file header) as a follow-on. We should also disable changing EC policy on a non-empty
file / dir in the first phase.



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