If your server has an SCSI hard drive and you intend to implement RAID on that server and you wish to add another SCSI hard drive to facilitate RAID you should connect the second SCSI hard drive to an empty SCSI port on your computer. SCSI stands for small computer system interface.
These are a set of ANSI (Amercian National Standards Institute) standard electronic interfaces that allow personal computers to communicate with hardware that includes such things as disk drives, tape drives, and CD-ROMs.
These are the most commonly used hard drives.