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From "philo vivero (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-1960) dfs.*.dir should not default to /tmp (or other typically volatile storage)
Date Thu, 19 May 2011 01:20:47 GMT
dfs.*.dir should not default to /tmp (or other typically volatile storage)
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                 Key: HDFS-1960
                 URL: https://issues.apache.org/jira/browse/HDFS-1960
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: data-node
    Affects Versions: 0.20.2
         Environment: *nix systems
            Reporter: philo vivero
            Priority: Critical


The hdfs-site.xml file possibly will not define one or both of:

dfs.name.dir
dfs.data.dir

If they are not specified, data is stored in /tmp. This is extremely dangerous. Rationale:
the cluster will work fine for days, possibly even weeks, before blocks will start to go missing.
Rebooting a datanode on common Linux systems will clear all the data from that node. There
is no documented way (that I'm aware of) to recover the situation. The cluster must be completely
obliterated and rebuilt from scratch.

Better reactions to the missing configuration parameters:

1. DataNode dies on startup and asks that these parameters be defined.
2. Default is /var/db/hadoop (or some other non-volatile storage location). Naturally, inability
to write into that directory leads to DataNode to die on startup, logging error.

The first solution would be most likely preferred by typical enterprise sysadmins. The second
solution is suboptimal (since /var/db/hadoop might not be the optimal location for the data)
but is still preferable to the current implementation, since it will less often lead to an
irretrievably corrupt cluster.

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