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https://issues.apache.org/jira/browse/HADOOP-3677?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12613384#action_12613384
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Konstantin Shvachko commented on HADOOP-3677:
---------------------------------------------
The advantages of the local upgrade (or as we also call it "version upgrade")
as opposed to a distributed upgrade are that it avoids both problems stated in
this jira, and also avoids thousands of warnings during data-node startup.
In my opinion, local/version upgrade is logically correct and is not a "hack"
at all, because each data-node can complete the upgrade on its own without
interacting with other data-nodes or the name-node. The distributed upgrade
should be used when such intercommunications are required. E.g. during the
crc-upgrade this was unavoidable.
The startup time will be the only disadvantage so the upgrade progress should
be logged every 20-30 seconds.
> Problems with generation stamp upgrade
> --------------------------------------
>
> Key: HADOOP-3677
> URL: https://issues.apache.org/jira/browse/HADOOP-3677
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.18.0
> Reporter: Konstantin Shvachko
> Assignee: Raghu Angadi
> Priority: Blocker
> Fix For: 0.18.0
>
>
> # The generation stamp upgrade renames blocks' meta-files so that the name
> contains the block generation stamp as stated in HADOOP-2656.
> If a data-node has blocks that do not belong to any files and the name-node
> asks the data-node to remove those blocks
> during or before the upgrade started the data-node will remove the blocks but
> not the meta-files because their names
> are still in the old format which is not recognized by the new code. So we
> can end up with a number of garbage files which
> will be hard to recognize that they are unused and the system will never
> remove them automatically.
> I think this should be handled by the upgrade code in the end, but may be it
> will be right to fix HADOOP-3002 for the 0.18 release,
> which will avoid scheduling block removal when the name-node is in safe-mode.
> # I was not able to get the upgrade -force option to work. This option lets
> the name-node proceed with a distributed upgrade even if
> the data-nodes are not able to complete their local upgrades. Did we test
> this feature at all for the generation stamp upgrade?
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