iam using hadoop apache 2.7.1
and i have configured data node directory to have multiple directories
<property>
<name>dfs.data.dir</name>
<value>/opt/hadoop/data_dir,file:///hdd/data_dir/</value>
<final>true</final>
</property>
according to this configuration writing file data should happens on both directories
/opt/hadoop/data_dir and file:///hdd/data_dir/ with same blocks names and on same sub directories names
but in my cluster this behavior is not happening some times it writes data blocks to
local directory /opt/hadoop/data_dir and some times it writes data blocks to
external hard directory file:///hdd/data_dir
what could be possible reasons and how to control this behavior