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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3368) Missing blocks due to bad DataNodes comming up and down.
Date Fri, 11 May 2012 22:23:50 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13273669#comment-13273669
] 

Konstantin Shvachko commented on HDFS-3368:
-------------------------------------------

> d01, do2, do3 are chosen for adding new block.

They are not chosen for new blocks. This is a different scenario.
do[1-3] went down long time ago (and all blocks were replicated out to other nodes), but were
not put into exclude list.
*On cluster restart* do[1-3] are brought up along with dn[1-3]. So for a brief period of time
the block had 6 replicas. 3 of them need to be deleted. Because of the current default policy
in place the replicas will be chosen to be deleted from dn[1-3], because those have less free
space. do[1-3] are flaky and die shortly after sending block reports on restart. So 10 minutes
later all 6 replicas will be gone.
Just as I described in my first comment. The bug is in the default policy. I'm not defining
a new one.
                
> Missing blocks due to bad DataNodes comming up and down.
> --------------------------------------------------------
>
>                 Key: HDFS-3368
>                 URL: https://issues.apache.org/jira/browse/HDFS-3368
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 0.22.0, 1.0.0, 2.0.0, 3.0.0
>            Reporter: Konstantin Shvachko
>            Assignee: Konstantin Shvachko
>         Attachments: blockDeletePolicy-0.22.patch, blockDeletePolicy-trunk.patch, blockDeletePolicy.patch
>
>
> All replicas of a block can be removed if bad DataNodes come up and down during cluster
restart resulting in data loss.

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