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From "Walter Su (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 Mon, 07 Sep 2015 08:23:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14733378#comment-14733378

Walter Su commented on HDFS-8833:

1. "Cannot createErasureCodingZone through a symlink to a " //DistributedFileSystem.java:2290
2. Iterating through xattrs is different now. Should use XAttrFeature.getXAttr(String) for
better performance.
final List<XAttr> xAttrs = inode.getXAttrFeature() == null ?  //FSDirErasureCodingOp.java:241
    new ArrayList<XAttr>(0)
    : inode.getXAttrFeature().getXAttrs();
for (XAttr xAttr : xAttrs) {
  if (XATTR_ERASURECODING_POLICY.equals(XAttrHelper.getPrefixedName(xAttr))) {
+1 after address 2 nits. #2 is not related though.

> Erasure coding: store EC schema and cell size in INodeFile and eliminate notion of EC
> -------------------------------------------------------------------------------------------
>                 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
>         Attachments: HDFS-8833-HDFS-7285-merge.00.patch, HDFS-8833-HDFS-7285-merge.01.patch,
HDFS-8833-HDFS-7285.02.patch, HDFS-8833-HDFS-7285.03.patch, HDFS-8833-HDFS-7285.04.patch,
HDFS-8833-HDFS-7285.05.patch, HDFS-8833-HDFS-7285.06.patch
> 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
> 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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