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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-11609) Some blocks can be permanently lost if nodes are decommissioned while dead
Date Fri, 31 Mar 2017 18:30:42 GMT
Kihwal Lee created HDFS-11609:

             Summary: Some blocks can be permanently lost if nodes are decommissioned while
                 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
            Priority: Critical

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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