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From "Alejandro Fernandez (JIRA)" <>
Subject [jira] [Created] (AMBARI-12252) Prevent datanode from creating datadir that becomes unmounted
Date Thu, 02 Jul 2015 04:49:04 GMT
Alejandro Fernandez created AMBARI-12252:

             Summary: Prevent datanode from creating datadir that becomes unmounted
                 Key: AMBARI-12252
             Project: Ambari
          Issue Type: Bug
          Components: ambari-agent
    Affects Versions: 1.7.0
            Reporter: Alejandro Fernandez
            Assignee: Alejandro Fernandez
            Priority: Critical
             Fix For: 2.1.0

This is related to AMBARI-7506

Ambari keeps track of a file, /etc/hadoop/conf/dfs_data_dir_mount.hist 
that contains a mapping of HDFS data dirs to the last known mount point.

This is used to detect when a data dir becomes unmounted, in order to prevent HDFS from writing
to the root partition.

Consider the example of a data node configured with these volumes: 

/dev/sda -> / 
/dev/sdb -> /grid/0
/dev/sdc -> /grid/1
/dev/sdd -> /grid/2

Typically, each /grid/#/ directory contains a data folder.
Today, if a data directory becomes unmounted, then the directory will not exist and Ambari
will not create it automatically. Ambari will simply log a warning, and update its cache with
the new mount point, which is /  ; that is the underlying bug.

If hdfs-site contains dfs.datanode.failed.volumes.tolerated with a value > 0, then DataNode
will tolerate the failure, otherwise, the DataNode will die.

Because Ambari will already have "/" in its cache file, the fact that it used to be mounted
in a non-root drive is lost, so next time DataNode is restarted, Ambari will create the data
dir which is now mounted on the root partition; this is really bad because HDFS will now fill
up the root drive.

The admin can still remount the partition, but then needs to restart DataNode so Ambari can
update its cache.

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