Sharepoint 2013 farm search indexing server hardware requirement

Hi everybody!

I am configuring a sharepoint 2013 farm. I have a SAN with 20TB for all my databases. I find in microsoft site sharepoint 2013 farm indexing server a 500GB hard disk requirement. I wanna to know is this hard requirement for Index databases???

If this hard is for index databases, which one give me better performance: I save index databases such as all other databases in farm onSAN or save index databases on hard disk of search index server itself???

Thanks for your time in advance...