Ficon Cascading - McDATA StorageWorks 2/140 - Director Switch Planning Manual

Planning Considerations for Fibre Channel Topologies
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FICON Cascading

McDATA Products in a SAN Environment - Planning Manual
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• Better fabric performance - As a connection between fabric
switches, a 10.2000 Gbps ISL delivers significantly greater
bandwidth. Fibre Channel devices that are not 10.2000 Gbps-
capable benefit from a higher-speed ISL, because slower traffic is
multiplexed and transmitted through the 10.2000 Gbps ISL.
• Additional port count - If additional ISL bandwidth is not
required for fabric performance, 10.2000 Gbps connectivity allows
the number of ISL connections to be reduced, thus yielding
additional director or switch ports for device connectivity.
When installing 10.2000 Gbps-capable fabric elements in a core-to-
edge topology, deploy the directors at the fabric core to provide
end-to-end high-speed ISL capability. If 10.2000 Gbps device
connectivity is required, attach the devices to the core director as Tier
1 devices. If possible, employ device locality by connecting 10.2000
Gbps devices to the same director.
The initial FICON architecture did not permit connection of multiple
directors or switches because the protocol specified a single byte for
the link (port) address definition in the input-output configuration
program (IOCP). The link address only defined the Port_ID for a
unique domain (director or switch).
The current FICON architecture provides two-byte addressing that
allows the IOCP to specify link (port) addresses for any number of
domains by including the domain address with the Port_ID. FICON
fabrics can now be configured using multiple directors and switches
(FICON cascading). In a cascaded FICON environment, at least three
Fibre Channel links are involved:
• The first link is between the FICON channel card (N_Port) of an
IBM eServer zSeries processor and a director or switch F_Port.
• The second link is an ISL between two director or switch E_Ports.
• The final link is from a director or switch F_Port to a FICON
adapter card (control unit N_Port) in a storage device, tape
device, or other peripheral.
These Fibre Channel links connect FICON fabric elements and
provide a physical transmission path between a channel and control
unit. Users may configure multiple ISLs between cascaded FICON
directors or switches to ensure redundancy and adequate bandwidth.