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Date: Tue, 11 Oct 2011 16:27:11 +0000 (UTC)
From: "M. C. Srivas (Commented) (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HDFS-2422) The NN should tolerate the same
 number of low-resource volumes as failed volumes
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    [ https://issues.apache.org/jira/browse/HDFS-2422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13125165#comment-13125165 ] 

M. C. Srivas commented on HDFS-2422:
------------------------------------

@Todd:  

With soft mounts, if the server goes down, I'd expect that the fsync would fail.  However, you wouldn't have any guarantee about what happened to all of the previous writes since the last successful fsync through the new failed fsync.  SOme of them might have succeeded and some might get lost.  Conceivably, some of them might get performed again when the server recovers.  So, I'd recommend that once you switch from one log to another, that you unlink the previous one when you get the chance before using it again, just to make sure you don't get any ghost writes showing up later.
                
> The NN should tolerate the same number of low-resource volumes as failed volumes
> --------------------------------------------------------------------------------
>
>                 Key: HDFS-2422
>                 URL: https://issues.apache.org/jira/browse/HDFS-2422
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 0.24.0
>            Reporter: Jeff Bean
>            Assignee: Aaron T. Myers
>             Fix For: 0.24.0
>
>         Attachments: HDFS-2422.patch
>
>
> We encountered a situation where the namenode dropped into safe mode after a temporary outage of an NFS mount.
> At 12:10 the NFS server goes offline
> Oct  8 12:10:05 <namenode> kernel: nfs: server <nfs host> not responding, timed out
> This caused the namenode to conclude resource issues:
> 2011-10-08 12:10:34,848 WARN org.apache.hadoop.hdfs.server.namenode.NameNodeResourceChecker: Space available on volume '<nfs host>' is 0, which is below the configured reserved amount 104857600
> Temporary loss of NFS mount shouldn't cause safemode.

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