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Date: Mon, 25 Aug 2014 18:08:59 +0000 (UTC)
From: "Colin Patrick McCabe (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12731235.1406852925284.5840.1408990139110@arcas>
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Subject: [jira] [Commented] (HDFS-6800) Determine how Datanode layout
 changes should interact with rolling upgrade
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    [ https://issues.apache.org/jira/browse/HDFS-6800?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14109424#comment-14109424 ] 

Colin Patrick McCabe commented on HDFS-6800:
--------------------------------------------

bq. Why couldn't we simply do the delete of the trash dir before the doRollback() call? If the trash removal succeeds and the doRollback() fails, it's not a problem, because we don't need the trash at all in the case where a previous directory is created.

That makes sense.

bq. Updated patch

I'm +1 on this... pending Jenkins, of course.  I will give it a day or two for others to review as well

> Determine how Datanode layout changes should interact with rolling upgrade
> --------------------------------------------------------------------------
>
>                 Key: HDFS-6800
>                 URL: https://issues.apache.org/jira/browse/HDFS-6800
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.6.0
>            Reporter: Colin Patrick McCabe
>            Assignee: James Thomas
>         Attachments: HDFS-6800.2.patch, HDFS-6800.3.patch, HDFS-6800.4.patch, HDFS-6800.5.patch, HDFS-6800.patch
>
>
> We need to handle attempts to rolling-upgrade the DataNode to a new storage directory layout.
> One approach is to disallow such upgrades.  If we choose this approach, we should make sure that the system administrator gets a helpful error message and a clean failure when trying to use rolling upgrade to a version that doesn't support it.  Based on the compatibility guarantees described in HDFS-5535, this would mean that *any* future DataNode layout changes would require a major version upgrade.
> Another approach would be to support rolling upgrade from an old DN storage layout to a new layout.  This approach requires us to change our documentation to explain to users that they should supply the {{\-rollback}} command on the command-line when re-starting the DataNodes during rolling rollback.  Currently the documentation just says to restart the DataNode normally.
> Another issue here is that the DataNode's usage message describes rollback options that no longer exist.  The help text says that the DN supports {{\-rollingupgrade rollback}}, but this option was removed by HDFS-6005.


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