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https://issues.apache.org/jira/browse/HADOOP-2186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12542617
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Konstantin Shvachko commented on HADOOP-2186:
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I agree the upgrade should benefit from multi-threaded link creation.
Does anybody have any experimental data on how many threads would be optimal
for that
kind of task taking into account both the number of hard drives and the number
of cores?
> DFS Upgrade should process dfs.data.dirs in parallel
> ----------------------------------------------------
>
> Key: HADOOP-2186
> URL: https://issues.apache.org/jira/browse/HADOOP-2186
> Project: Hadoop
> Issue Type: Improvement
> Components: dfs
> Affects Versions: 0.15.0
> Reporter: Stu Hood
> Priority: Minor
>
> I just upgraded from 0.14.2 to 0.15.0, and things went very smoothly, if a
> little slowly.
> The main reason the upgrade took so long was the block upgrades on the
> datanodes. Each of our datanodes has 3 drives listed for the dfs.data.dir
> parameter. From looking at the logs, it is fairly clear that the upgrade
> procedure does not attempt to upgrade all listed dfs.data.dir's in parallel.
> I think even if all of your dfs.data.dir's are on the same physical device,
> there would still be an advantage to performing the upgrade process in
> parallel. The less downtime, the better: especially if it is potentially 20
> minutes versus 60 minutes.
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