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https://issues.apache.org/jira/browse/HDFS-6440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14531238#comment-14531238
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Jesse Yates commented on HDFS-6440:
-----------------------------------
[~atm] thanks for the feedback. I'm working on rebasing on trunk and addressing
your comments (hopefully a patch by tomorrow), but a couple of
comments/questions first:
bq. Rolling upgrades/downgrades/rollbacks.
I'm not sure how we would test this when needing to change the structure of the
FS to support more than 2 NNs. Would you recommend (1) recognizing the old
layout and then (2) transfering it into the new layout? The reason this seems
silly (to me) is that the layout is only enforced by the way the minicluster is
used/setup, rather than the way things would actually be run. By moving things
into the appropriate directories per-nn, but keeping everything else below that
the same, I think we keep the same upgrade properties but don't need to do the
above contrived/synthetic "upgrade".
bq. What's a "fresh cluster" vs. a "running cluster" in this sense?
Maybe some salesforce terminology leak here. "Fresh" would be one where you
just formatted the primary NN and are bootstrapping the other NNs from that
layout. "Running" would be when bringing up a SNN after some sort of failure
and it has an unformatted fs - then it can pull from any node in the cluster.
As an SNN it would then be able to catch up by tailing the ANN.
I'll update the comment.
bq. is changing the value of FAILOVER_SEED going to do anything, given that
it's only ever read at the static initialization of the failoverRandom?
Yes, it for when there is an error and you want to run the exact sequence of
failovers again in the test. Minor helper, but can be useful when trying to
track down ordering dependency issues (which there shoudn't be, but sometimes
these things can creep in).
Otherwise, everything else seems completely reasonable. Thanks!
> Support more than 2 NameNodes
> -----------------------------
>
> Key: HDFS-6440
> URL: https://issues.apache.org/jira/browse/HDFS-6440
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: auto-failover, ha, namenode
> Affects Versions: 2.4.0
> Reporter: Jesse Yates
> Assignee: Jesse Yates
> Attachments: Multiple-Standby-NameNodes_V1.pdf,
> hdfs-6440-cdh-4.5-full.patch, hdfs-6440-trunk-v1.patch,
> hdfs-6440-trunk-v1.patch, hdfs-multiple-snn-trunk-v0.patch
>
>
> Most of the work is already done to support more than 2 NameNodes (one
> active, one standby). This would be the last bit to support running multiple
> _standby_ NameNodes; one of the standbys should be available for fail-over.
> Mostly, this is a matter of updating how we parse configurations, some
> complexity around managing the checkpointing, and updating a whole lot of
> tests.
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