HP StorageWorks 2/24 FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Env - Page 138

Planning Considerations for Fibre Channel Topologies 3 • 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 Gbpscapable 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-toedge 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. FICON Cascading 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. 3-52 McDATA Products in a SAN Environment - Planning Manual