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https://issues.apache.org/jira/browse/HDFS-528?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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dhruba borthakur updated HDFS-528:
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Status: Open (was: Patch Available)
It appears that this functionality can be achieved by some code outside the
namenode.
1. start the NN with a dfs.safemode.threshold.pct 1.5 i.e. NN will never exit
safemode by itself.
2. write a script that periodically invokes "bin/hadoop dfsadmin -report" and
counts the number of datanodes that have checked in with the NN.
3. The script can explicitly exit safemode whenever it desires.
This approach allows different policies of when-to-exit-safemode be implemented
outside the NN.
If you agree, then we can make this JIRA expose a new API from the NN that
exposes the safeBlockCount and totalBlockCount from the NN.
> Add ability for safemode to wait for a minimum number of live datanodes
> -----------------------------------------------------------------------
>
> Key: HDFS-528
> URL: https://issues.apache.org/jira/browse/HDFS-528
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: scripts
> Affects Versions: 0.22.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Attachments: hdfs-528-v2.txt, hdfs-528-v3.txt, hdfs-528.txt,
> hdfs-528.txt
>
>
> When starting up a fresh cluster programatically, users often want to wait
> until DFS is "writable" before continuing in a script. "dfsadmin -safemode
> wait" doesn't quite work for this on a completely fresh cluster, since when
> there are 0 blocks on the system, 100% of them are accounted for before any
> DNs have reported.
> This JIRA is to add a command which waits until a certain number of DNs have
> reported as alive to the NN.
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