HP Mainframe Connectivity Design Guide

Director models
Entry switches in a FICON SAN are typically director-class products (up to 256 ports). FICON
switch-class products are used in small data centers with only CUs or a limited number of attached
mainframe channels. For supported director models, see the following:
• “B-series FICON directors and fabric rules” (page 29)
• “C-series FICON directors and fabric rules” (page 46)
• “McDATA FICON directors and fabric rules” (page 63)
Benefits
The benefits of a cascaded fabric are as follows:
• Ability to connect mainframes and CUs in diverse geographic locations
• Ability to connect two sites using fewer ISLs instead of several FICON channels
• Ease of scalability for increased mainframe and storage connectivity
• Shared backup and management support
• Cost efficiency due to the large number of FICON ports available
Recommended ISL ratios
When determining the required number of ISLs between cascaded FICON directors, consider the
following factors to ensure that data traffic is not blocked at the ISL:
• Speed of the FICON channels on the mainframe
• Speed of the FICON ports on the CUs
• Anticipated throughput of each FICON port on the mainframe and the CU
HP recommends that a FICON SAN have an average utilization of 50% on each FICON port,
allowing for redundancy and the maintenance of production data throughput in the event of a port
failure. For more information, see “FICON SAN best practices” (page 154).
HP recommends the following for a FICON SAN:
• Use a minimum of two ISLs between each pair of cascaded FICON directors.
• Use ISLs with the same or higher-speed ports as the ingress/egress FICON ports. For example,
do not use a 2 Gb/s ISL to support 4 or 8 Gb/s ingress/egress ports.
• If the ISLs are rated at the same speed as the ingress/egress FICON ports, and the average
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utilization is less than 50%, then use one ISL for every four FICON ports.
• If the ISLs are rated at the same speed as the ingress/egress FICON ports, and the average
utilization is greater than 50%, then increase the number of ISLs accordingly (one ISL for every
two or three ingress/egress FICON ports).
• If the ISLs are rated at a higher speed than the ingress/egress FICON ports, then consider the
total and average anticipated throughput for the ISL.
• Use peak throughput values whenever possible to ensure that the ISLs can manage the volume
during peak times.
• Use higher speed ports (such as 8 Gb/s or 16 Gb/s ports) for ISLs whenever possible.
18 FICON SAN fabric topologies