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From "Vinayakumar B (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4015) Safemode should count and report orphaned blocks
Date Mon, 21 Nov 2016 10:41:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15683168#comment-15683168

Vinayakumar B commented on HDFS-4015:

Should this be marked as incompatible change?
Earlier "dfsadmin -safemode leave" was leaving the safemode.
Now expects "-forceExit" also if there are any future bytes detected.
Please correct If I am missing something here.

> Safemode should count and report orphaned blocks
> ------------------------------------------------
>                 Key: HDFS-4015
>                 URL: https://issues.apache.org/jira/browse/HDFS-4015
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 3.0.0-alpha1
>            Reporter: Todd Lipcon
>            Assignee: Anu Engineer
>             Fix For: 2.8.0, 3.0.0-alpha1
>         Attachments: HDFS-4015.001.patch, HDFS-4015.002.patch, HDFS-4015.003.patch, HDFS-4015.004.patch,
HDFS-4015.005.patch, HDFS-4015.006.patch, HDFS-4015.007.patch
> The safemode status currently reports the number of unique reported blocks compared to
the total number of blocks referenced by the namespace. However, it does not report the inverse:
blocks which are reported by datanodes but not referenced by the namespace.
> In the case that an admin accidentally starts up from an old image, this can be confusing:
safemode and fsck will show "corrupt files", which are the files which actually have been
deleted but got resurrected by restarting from the old image. This will convince them that
they can safely force leave safemode and remove these files -- after all, they know that those
files should really have been deleted. However, they're not aware that leaving safemode will
also unrecoverably delete a bunch of other block files which have been orphaned due to the
namespace rollback.
> I'd like to consider reporting something like: "900000 of expected 1000000 blocks have
been reported. Additionally, 10000 blocks have been reported which do not correspond to any
file in the namespace. Forcing exit of safemode will unrecoverably remove those data blocks"
> Whether this statistic is also used for some kind of "inverse safe mode" is the logical
next step, but just reporting it as a warning seems easy enough to accomplish and worth doing.

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