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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6800) Determine how Datanode layout changes should interact with rolling upgrade
Date Mon, 25 Aug 2014 18:08:59 GMT

    [ 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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