4.6 Chapter Summary

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.



Designing Storage Area Networks(c) A Practical Reference for Implementing Fibre Channel and IP SANs
Designing Storage Area Networks: A Practical Reference for Implementing Fibre Channel and IP SANs (2nd Edition)
ISBN: 0321136500
EAN: 2147483647
Year: 2003
Pages: 171
Authors: Tom Clark

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