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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7230) Support rolling downgrade
Date Tue, 14 Oct 2014 00:41:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14170306#comment-14170306
] 

Tsz Wo Nicholas Sze commented on HDFS-7230:
-------------------------------------------

Same as downgrade, rolling downgrade requires the same NAMENODE_LAYOUT_VERSION and the same
DATANODE_LAYOUT_VERSION.  Although there is no layout change, a cluster may not be downgraded
using the same rolling upgrade procedure since protocols may change in a backward compatible
manner but not forward compatible, i.e. old DNs can talk to the new NNs but new DNs may not
be able to talk the old NNs.


> Support rolling downgrade
> -------------------------
>
>                 Key: HDFS-7230
>                 URL: https://issues.apache.org/jira/browse/HDFS-7230
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Tsz Wo Nicholas Sze
>            Assignee: Tsz Wo Nicholas Sze
>
> HDFS-5535 made a lot of improvement on rolling upgrade.  It also added the cluster downgrade
feature.  However, the downgrade described in HDFS-5535 requires cluster downtime.  In this
JIRA, we discuss how to do rolling downgrade, i.e. downgrade without downtime.



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