CertiGuide to A+ (A+ 4 Real)  9  Chapter 10: The Small Computer System Interface, SCSI

ISCSI HBAs 1 Serial Advanced Technology Attachment (SATA)

Fibre Channel¹³³ is a communications protocol designed to meet the require-ments of the ever-increasing demand for high performance data transfer. Fibre Channel combines the benefits of both channel and network technolo-gies. A channel is a closed, direct, structured, and predictable mechanism for transmitting data between relatively few points with low overhead. By contrast, a Network is a mixture of different nodes (like workstations, file servers or peripherals) with its own protocol that supports interaction be-tween these nodes. A network has high overhead because it is software-intensive, so it is slower than a channel.

Once a channel is set up, there is very little decision-making needed, thus allowing for a high-speed, hardware intensive environment. Channels are commonly used to connect peripheral devices such as disk drives, printers, tape drives, etc. to a workstation or server. Fibre Channel is a high performance serial link that uses SCSI as an upper layer protocol.

The benefits of mapping the SCSI command set onto Fibre Channel include:

• Faster speed (up to 2 Gbit)
  
  
• More devices can be connected together (up to 16 million devices in an ex-tended SAN)
  
  
• Larger distance allowed between devices (up to 10 km)

Fibre Channel, which can handle frames of any size, is an ANSI standard that defines the data link interface specification for transmissions over fiber optic and coaxial cables. The technology, implemented in hubs, switches, and host bus adapters, is mainly targeted for handling the transfer of large files at high speeds of up to 2 Gbit/sec. and distances of up to 10 km. It is com-monly used in storage area networks. Being able to access mass storage devices quicker and from greater distances is very attractive to such applica-tions as multimedia, medical imaging, and scientific visualization. Because of the greater distances allowed, Fibre Channel has advantages in disaster recovery situations as storage devices can be placed remotely.

ISCSI HBAs 1 Serial Advanced Technology Attachment (SATA)