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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-2585) Automatic namespace recovery from the secondary image.
Date Sat, 12 Jan 2008 00:24:34 GMT
Automatic namespace recovery from the secondary image.
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                 Key: HADOOP-2585
                 URL: https://issues.apache.org/jira/browse/HADOOP-2585
             Project: Hadoop
          Issue Type: New Feature
          Components: dfs
    Affects Versions: 0.15.0
            Reporter: Konstantin Shvachko


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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