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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-11609) Some blocks can be permanently lost if nodes are decommissioned while dead
Date Mon, 03 Apr 2017 22:19:41 GMT

     [ https://issues.apache.org/jira/browse/HDFS-11609?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kihwal Lee updated HDFS-11609:
------------------------------
    Attachment: HDFS-11609.trunk.patch

> Some blocks can be permanently lost if nodes are decommissioned while dead
> --------------------------------------------------------------------------
>
>                 Key: HDFS-11609
>                 URL: https://issues.apache.org/jira/browse/HDFS-11609
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.7.0
>            Reporter: Kihwal Lee
>            Assignee: Kihwal Lee
>            Priority: Critical
>         Attachments: HDFS-11609.trunk.patch
>
>
> When all the nodes containing a replica of a block are decommissioned while they are
dead, they get decommissioned right away even if there are missing blocks. This behavior was
introduced by HDFS-7374.
> The problem starts when those decommissioned nodes are brought back online. The namenode
no longer shows missing blocks, which creates a false sense of cluster health. When the decommissioned
nodes are removed and reformatted, the block data is permanently lost. The namenode will report
missing blocks after the heartbeat recheck interval (e.g. 10 minutes) from the moment the
last node is taken down.
> There are multiple issues in the code. As some cause different behaviors in testing vs.
production, it took a while to reproduce it in a unit test. I will present analysis and proposal
soon.



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