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Date: Tue, 11 Oct 2011 07:04:30 +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=13124766#comment-13124766 ] 

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

Konstantin and Todd, should the timeout be short, or long?

>From the NFS FAQ ... http://nfs.sourceforge.net/#faq_e4 ... soft mounts can cause silent data corruption, even in the middle of a file, when a brief outage occurs. Thus, during recovery, even though the edits-log looks up-to-date, it might contain bad pages in the middle.

If you wish to use soft-mounts, then the recovery process should verify all the logs before picking one of them to use for replay. (I am not sure if there are CRCs on every record of the edits-log .. are there?)

Otherwise, with soft-mounts, you will hit issues like HDFS-1382.


                
> 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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