EhCache memory region

I have a JEE application and making use of EhCache.

I have one question, where does EhCache store its elements ? Is it at the java heap memory or it have separate region to store it.

I need to store a huge amount of data, one way is to store this at session level. But making session unnecessary heavy is not a good idea also it needs to be shared among various users. Another way is to store it at EhCache level. So if I store it at EhCache level, does it take the memory from heap and cause some performance problem.

On my EhCache.xml below is the diskstore property value:

 <diskStore
    path="java.io.tmpdir/casinomodule/ehcache" />

Please suggest.