[jira] [Created] (AMBARI-12267) Ambari to improve tracking of data dirs becoming unmounted.

["Alejandro Fernandez (JIRA)" <ji...@apache.org>]

Alejandro Fernandez created AMBARI-12267:
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             Summary: Ambari to improve tracking of data dirs becoming unmounted.
                 Key: AMBARI-12267
                 URL: https://issues.apache.org/jira/browse/AMBARI-12267
             Project: Ambari
          Issue Type: Story
          Components: ambari-agent
    Affects Versions: 2.0.0
            Reporter: Alejandro Fernandez
            Assignee: Alejandro Fernandez
             Fix For: 2.2.0


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.

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

In AMBARI-12252, I fixed a bug so that Ambari would prevent an unmounted drive from allowing HDFS to write to the root partition.
However, this approach relies on the /etc/hadoop/conf/dfs_data_dir_mount.hist file existing, and the original configuration being correct.

The ideal way to fix this is,
* Track which data dirs the admin wants mounted on a non-root partition. If the admin wishes all data dirs to be on non-root mounts, but the initial install is incorrect, then this should be reported as a problem.
* Keep the history of the mount points in the database. Today, if the cache file is deleted or the host reimaged, then this information is lost.
* Introduce a new state between FAILED and COMPLETED, such as COMPLETED_WITH_ERRORS, that will allow tasks to look differently in the UI, so the user can clearly detect when a critical but non fatal error happened.
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