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https://issues.apache.org/jira/browse/HDFS-12420?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16165515#comment-16165515
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Allen Wittenauer commented on HDFS-12420:
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bq. current format functionality is broken itself. It deletes the metadata
while doing nothing about the data stored in data-nodes.
Just like mkfs. And just like it, the fact that it doesn't delete the actual
data is a feature, not a bug. If I restore the fsimage back then my data
should come back too. (mostly... new data ofc is likely to be missing, etc)
It's why making a copy of the fsimage is Hadoop Ops 101.
Some key advice I give to admins: you can try to prevent mistakes, but they'll
still happen despite your best efforts. After low hanging warnings, the energy
is better spent on how to quickly recover. But that's a problem that's outside
of the core code.
For the record, yes, I've made HUGE mistakes like this in my career. Every
admin has. In my case, I brought down an entire hospital once. Even with that
experience, I still think requiring metadata deletion outside of the tool set
is waaaaay overkill.
bq. may be being able to tag a cluster as "production" like discussed above is
a better idea?
Yeah, sure, whatever. All that's going to happen is:
{code}
hdfs --config /tmp/mymodifiedconfig namenode -format -force
{code}
If a user is too lazy/impatient/distracted to check that they are on a live
system before hitting y, they'll just change the flag and then format. But if
that makes folks happy, fine. It still sounds like the console output needs
some work though if a user couldn't "see" it. (Not sure I agree with that
either, but whatever.)
BTW, a quick search for how the equivalent problem is solved in databases is
interesting. Almost all of them that I looked at: don't give the user access.
So yes, enough rope to hang themselves seems to be the expectation
operationally.
> Disable Namenode format when data already exists
> ------------------------------------------------
>
> Key: HDFS-12420
> URL: https://issues.apache.org/jira/browse/HDFS-12420
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Ajay Kumar
> Assignee: Ajay Kumar
> Attachments: HDFS-12420.01.patch, HDFS-12420.02.patch
>
>
> Disable NameNode format to avoid accidental formatting of Namenode in
> production cluster. If someone really wants to delete the complete fsImage,
> they can first delete the metadata dir and then run {code} hdfs namenode
> -format{code} manually.
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