A system includes a number of hard disk drives and a controller. Each hard disk drive is selected from a number of different hard disk drive types. Each hard disk drive type has a different speed at which the hard disk drives of the hard disk drive type rotate to read and write data. At least one of the hard disk drives is of a different hard disk drive type than at least one other of the hard disk drives. The controller, responsive to a request to write particular data to the hard disk drives, is to select a given hard disk drive of the hard disk drives based on a type of the particular data, and is to write the particular data to the given hard disk drive.