Database servers frequently read and write data to your hard drives. So increasing the speed at which data can be written and retrieved has a big effect on performance. Many people recommend SSD (Solid State Drives) for databases with high I/O requirements, as data can be written and read faster. However SSD comes at a higher price than SATA.
Whatever your choice, it is generally recommended that you split server elements across several drives on your dedicated server. This might mean a separate disk for your operating system, data files, log files, and databases. Finally, each element may be better suited to a particular RAID, to improve redundancy and performance.