Fibre Channel - Computer Busses - page 213

The networking options include:
• Point-to-point connections - these are point-to-point connections, and are not connected
as a ring.
• Switch connections.
• Hub connections - these connect onto a ring, with the 'ring out' of each switch con-
nected to the 'ring in' of the next, and so on. This makes a ring with devices connecting
to the hub (and not to the ring).
• Fibre channel storage system - this contains hot swap disks with a 100 MB/s data trans-
fer.
• SCSI RAID connection.
• Cluster connection - workstations plug directly to a hub. The hub detects if a work-
station is connected and automatically connects it to the ring.
• WAN connection - connection to WAN, such as ATM, STM or FDDI.
12.5 Storage Devices and storage area networks
One of the largest uses of fibre channel is likely to be in storage interfaces. It has many ad-
vantages over SCSI, including distance, bandwidth, scalability and reliability. Many manu-
facturers now provide RAID-based systems with Fibre channel.
A good area of application for Fibre channel is in storage area networks. These typically
contain one or more servers, which also connect to one or more storage systems. These stor-
age systems could be RAID, tape back-up, CD-ROMs or disk drives.
In a fibre channel network, SCSI devices are interfaced to the Fibre channel using a Fibre
channel to SCSI bridge, and IP is used for server to server and client/server communications.
Fibre channel disks have a back plane with a built-in fibre channel loop. At each disk
location in the back-plane loop is a port bypass circuit which permits hot swapping of disks.
If a disk is not present, the circuit automatically closes the loop. When a disk is inserted, the
loop is opened to connect to the disk.
12.6 Networks
Fibre channel has many advantages over traditional networking technologies, these include:
• Automatic configuration - support for automatic configuration protocols, such as ARP,
RARP and other self-discovery protocols.
• Automatic self-discovery of Fibre channel topology.
• Confirmed delivery - this enhances reliability, and does not rely on higher-level proto-
cols to confirm delivery.
• Efficient, high-bandwidth low-latency transfers - this uses a variable length frame (up to
2 kB). It uses an efficient protocol which only has an overhead of up to 100 bytes.