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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2585) Automatic namespace recovery from the secondary image.
Date Fri, 11 Apr 2008 06:52:09 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12587864#action_12587864
] 

dhruba borthakur commented on HADOOP-2585:
------------------------------------------

Code looks good. Only one comment:
1. The patch makes rollEditLog() return a WritableComparable . It might be better to make
it return an object of type CheckpointSignature.



> Automatic namespace recovery from the secondary image.
> ------------------------------------------------------
>
>                 Key: HADOOP-2585
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2585
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>    Affects Versions: 0.16.0
>            Reporter: Konstantin Shvachko
>            Assignee: Konstantin Shvachko
>             Fix For: 0.18.0
>
>         Attachments: SecondaryStorage.patch, SecondaryStorage.patch
>
>
> Hadoop has a three way (configuration controlled) protection from loosing the namespace
image.
> # image can be replicated on different hard-drives of the same node;
> # image can be replicated on a nfs mounted drive on an independent node;
> # a stale replica of the image is created during periodic checkpointing and stored on
the secondary name-node.
> Currently during startup the name-node examines all configured storage directories, selects
the
> most up to date image, reads it, merges with the corresponding edits, and writes to the
new image back 
> into all storage directories. Everything is done automatically.
> If due to multiple hardware failures none of those images on mounted hard drives (local
or remote) 
> are available the secondary image although stale (up to one hour old by default) can
be still 
> used in order to recover the majority of the file system data.
> Currently one can reconstruct a valid name-node image from the secondary one manually.
> It would be nice to support an automatic recovery.

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