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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-124) don't permit two datanodes to run from same dfs.data.dir
Date Tue, 09 May 2006 01:16:22 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-124?page=comments#action_12378550 ] 

Konstantin Shvachko commented on HADOOP-124:
--------------------------------------------

There is a problem with shutting down the old datanode when the new one starts.
The new datanode must be sure the old one is gone before taking over.

I think a datanode should merely keep a FileLock in the dfs.data.dir while it is running.
In this case the new node will not be able to start with the same data directory.
Is that the problem we are trying to solve here?


> don't permit two datanodes to run from same dfs.data.dir
> --------------------------------------------------------
>
>          Key: HADOOP-124
>          URL: http://issues.apache.org/jira/browse/HADOOP-124
>      Project: Hadoop
>         Type: Bug

>   Components: dfs
>     Versions: 0.2
>  Environment: ~30 node cluster
>     Reporter: Bryan Pendleton
>     Assignee: Konstantin Shvachko
>     Priority: Critical
>      Fix For: 0.3

>
> DFS files are still rotting.
> I suspect that there's a problem with block accounting/detecting identical hosts in the
namenode. I have 30 physical nodes, with various numbers of local disks, meaning that my current
'bin/hadoop dfs -report" shows 80 nodes after a full restart. However, when I discovered the
 problem (which resulted in losing about 500gb worth of temporary data because of missing
blocks in some of the larger chunks) -report showed 96 nodes. I suspect somehow there were
extra datanodes running against the same paths, and that the namenode was counting those as
replicated instances, which then showed up over-replicated, and one of them was told to delete
its local block, leading to the block actually getting lost.
> I will debug it more the next time the situation arises. This is at least the 5th time
I've had a large amount of file data "rot" in DFS since January.

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