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From "Arpit Agarwal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10301) BlockReport retransmissions may lead to storages falsely being declared zombie if storage report processing happens out of order
Date Wed, 14 Sep 2016 21:34:21 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15491507#comment-15491507
] 

Arpit Agarwal commented on HDFS-10301:
--------------------------------------

I don't think it is safe to remove storages (and hence blocks) when the NameNode doesn't have
up to date block replica state because the block->storage mapping on the NameNode can be
stale e.g. due to disk balancer moving replicas; or due to the way VolumeChoosingPolicy picks
storages for new blocks.

> BlockReport retransmissions may lead to storages falsely being declared zombie if storage
report processing happens out of order
> --------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-10301
>                 URL: https://issues.apache.org/jira/browse/HDFS-10301
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.6.1
>            Reporter: Konstantin Shvachko
>            Assignee: Vinitha Reddy Gankidi
>            Priority: Critical
>         Attachments: HDFS-10301.002.patch, HDFS-10301.003.patch, HDFS-10301.004.patch,
HDFS-10301.005.patch, HDFS-10301.006.patch, HDFS-10301.007.patch, HDFS-10301.008.patch, HDFS-10301.009.patch,
HDFS-10301.01.patch, HDFS-10301.010.patch, HDFS-10301.011.patch, HDFS-10301.012.patch, HDFS-10301.013.patch,
HDFS-10301.014.patch, HDFS-10301.branch-2.7.patch, HDFS-10301.branch-2.patch, HDFS-10301.sample.patch,
zombieStorageLogs.rtf
>
>
> When NameNode is busy a DataNode can timeout sending a block report. Then it sends the
block report again. Then NameNode while process these two reports at the same time can interleave
processing storages from different reports. This screws up the blockReportId field, which
makes NameNode think that some storages are zombie. Replicas from zombie storages are immediately
removed, causing missing blocks.



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