SCSI (pronounced as scuzzy) is an industry standard protocol for attaching various I/O peripherals such as printers, scanners, tape drives, and storage devices. The most common SCSI devices are disks and tape libraries.

SCSI has evolved from parallel, daisy-chained SCSI to serially attached SCSI (SAS). Older parallel SCSI specifications are defined as Ultra-1, Ultra-2, Ultra-3, Ultra-320, and Ultra-640, whereas the new SAS specifications are defined as SAS 1.0, 2.0, and 3.0. These specifications differ in speed and other performance enhancements. SCSI hard disks are superior in terms of performance and reliability as compared with ATA (PATA and SATA) drives. SCSI drives are commonly used in enterprise-grade SANs because of their reliability and speed.

In the SAN world, SCSI is the core protocol to connect raw hard disk storage with the servers. In order to control remote storage with the SCSI protocol, different technologies are used as wrappers to encapsulate these commands. These primarily include FC and iSCSI. In the following sections, we'll briefly review these technologies.