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From "Aaron T. Myers (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2422) The NN should tolerate the same number of low-resource volumes as failed volumes
Date Mon, 10 Oct 2011 23:14:31 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13124558#comment-13124558

Aaron T. Myers commented on HDFS-2422:

Thanks for the comments Milind.

bq. 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.).

Ah, I misunderstood your earlier comment. That seems reasonable to me. I've filed HDFS-2430
to address this issue.

bq. 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.

Do you disagree with the reasoning Eli posted in the comment I linked to earlier? I found
his argument quite compelling. If so, we should probably file a separate JIRA for that, along
the lines of "The NN should automatically leave SM if sufficient resources become available
again after they were previously low" and continue the discussion there.
> 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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