I would recommend to use a fast SSD for the System and mount a extra disk for Media. Additionally, I would invest in multiple HDD, since with a good RAID setup, you can speed up the reading and writing of files (simultaneously read and write on multiple drives) and if one of your drives dies (which server drives will after some years) you can replace one or even two (depending on RAID setup) HDDs without loosing data (there will be time needed to restore the files, depending on your RAID setup)