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https://issues.apache.org/jira/browse/HDFS-4015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14936086#comment-14936086
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Arpit Agarwal commented on HDFS-4015:
-------------------------------------
Hi [~anu], thanks for this improvement. Few comments below, I haven't reviewed
the test case yet.
# ClientProtocol.java:729: Perhaps we can describe it as "bytes that are at
risk for deletion."?
# DFSAdmin.java:474: This can happen even without blocks with future generation
stamps e.g. DN is restarted after a long downtime and reports blocks for
deleted files.
# FSNamesystem.java:4438: For turn-off tip, should we check
{{getBytesInFuture}} after the threshold of reported blocks isreached? One
potential issue is that the administrator may see this message and immediately
run {{-forceExit}} even before block thresholds are reached.
# FSNamesystem.java:4445: "you are ok with data loss." might also be confusing.
Perhaps we can say "if you are certain that the NameNode was started with the
correct FsImage and edit logs."
# FSNamesystem.java:4631: Not sure how this works. leaveSafeMode will just
return {{if (isInStartupSafeMode() && (blockManager.getBytesInFuture() > 0))}}
Comments also posted at
https://github.com/arp7/hadoop/commit/f16f4525a9a814f0945e76af55ad06b5fc18ecb7
> 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
> Reporter: Todd Lipcon
> Assignee: Anu Engineer
> Attachments: HDFS-4015.001.patch, dfsAdmin-report_with_forceExit.png,
> dfsHealth.html.message.png
>
>
> 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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