Point-to-Point
Point-to-Point Fibre Channel is a dedicated connection between two N_Ports, typically a server and a disk.
Arbitrated Loop
Arbitrated loop is a ring topology supporting as many as 127 attachments on a shared, 100MBps bandwidth.
Loop hubs collapse the ring topology into a physical star configuration.
Arbitrated loop physical addresses (AL_PAs) are dynamically assigned, 1-byte identifiers.
Loop initialization ensures that each device has a unique AL_PA.
Following loop initialization, initiators (servers) discover targets (disks) via port login.
The loop port state machine monitors activity on the loop and is responsible for initialization and loop access.
Access to the loop is gained through arbitration. A fairness algorithm ensures that all participants are allowed utilization of the loop.
Arbitrated loop is nonbroadcast; the recipient of frames removes them from the loop.
Total loop population should be application-driven.
Private loop devices do not support fabric services; public loop devices will attempt fabric login to obtain a loop identifier.
Loops support 10km links, but any long haul will incur propagation delay for all loop transactions.
Managed loop hubs should be used for mission-critical environments.
Redundant loops provide duplicate data paths and hardware for failover.
Fabrics
A fabric is one or more Fibre Channel switches; each fabric port provides full bandwidth to the attached device.
Fabric addressing allows for more than 15 million unique identifiers.
The 3-byte port address is divided into domain, area, and port.
Fabrics can be configured in a meshed topology to provide redundant links.
An N_Port performs fabric login to establish a session with the fabric switch.
An N_Port may register its World-Wide Name and service parameters with the Simple Name Server to facilitate discovery of targets.
Registered State Change Notification allows a device to be notified if a communicating partner leaves or reenters the fabric.
Some fabric switches may provide support for private loop devices and allow public devices to access them.
Zoning allows segregation of devices by port or World-Wide Name.
E_Port connections enable scaling of a fabric to provide more ports.
The Fabric Shortest Path First protocol determines the best network path based on available bandwidth between switches.
The principal switch ensures that each switch has a unique Domain_ID.
Principal switch selection may be disruptive or nondisruptive, depending on how new switches are introduced to the fabric.
Fabrics and Loops
Fabrics and loop hubs can be combined to create an integrated SAN.
Leveraging loop attachment to a fabric enables discrete allocation of bandwidth and cost-effective utilization of switch ports.