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https://issues.apache.org/jira/browse/SPARK-6112?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14606612#comment-14606612
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Arpit Agarwal commented on SPARK-6112:
--------------------------------------

Seems to work fine with Spark 1.4.0 + Hadoop 2.7 also. Are your storage types 
tagged correctly in hdfs-site.xml? You will need to tag the RAM disk path in 
{{dfs.datanode.data.dir}} with \[RAM_DISK\]. e.g. from my test machine.
{code}
  <property>
    <name>dfs.data.dir</name>
    <value>[RAM_DISK]/mnt/tmpfs/hadoop/data,[DISK]/mnt/sdb/hadoop/data</value>
  </property>
{code}
You can test without spark by simply copying a file to the target directory 
with the policy and verifying its block files go to RAM disk.

> Provide external block store support through HDFS RAM_DISK
> ----------------------------------------------------------
>
>                 Key: SPARK-6112
>                 URL: https://issues.apache.org/jira/browse/SPARK-6112
>             Project: Spark
>          Issue Type: New Feature
>          Components: Block Manager
>            Reporter: Zhan Zhang
>         Attachments: SparkOffheapsupportbyHDFS.pdf
>
>
> HDFS Lazy_Persist policy provide possibility to cache the RDD off_heap in 
> hdfs. We may want to provide similar capacity to Tachyon by leveraging hdfs 
> RAM_DISK feature, if the user environment does not have tachyon deployed. 
> With this feature, it potentially provides possibility to share RDD in memory 
> across different jobs and even share with jobs other than spark, and avoid 
> the RDD recomputation if executors crash. 



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