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Date: Mon, 10 Oct 2011 23:04:30 +0000 (UTC)
From: "Milind Bhandarkar (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=13124552#comment-13124552 ] 

Milind Bhandarkar commented on HDFS-2422:
-----------------------------------------

Aaron, the failed volume policy should ensure that at least two volumes are up when writing edit logs. If it were only writing to one volume, and staying writable, then there is a time period when there is a single up-to-date replica of edit logs that can fail and lose modifications (that is why I said the window opens for losing data, anot that it will definitely lose data.).

re: automatically coming out of safemode, I think transient unavailability of a volume, and a volume being low on disk space should be treated differently. While the second case requires admin intervention, the first case does not.
                
> 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
>         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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