HP Mainframe Connectivity Design Guide

Level 4: multiple fabrics and device paths (NSPOF)
Level 4 provides multiple data paths between mainframes and storage systems, but unlike level 3,
the paths connect to physically separate fabrics . This level ensures the highest availability with
NSPOF protection. If a director port, mainframe channel, or storage system port failure occurs,
data is automatically rerouted through the alternate fabric and there is no interruption in mainframe
I/O activity. Figure 7 (page 23) shows a level 4 fabric.
Level 4 minimizes vulnerability to fabric failures (for example, improper director replacement,
incorrect fabric configuration settings, or a fabric service failure). Level 4 also provides the highest
level of performance and a higher number of available ports, since all fabrics can be accessed
simultaneously during normal operations.
Figure 7 Level 4: multiple fabrics and device paths (NSPOF)
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Considerations
When choosing a data availability level, you must consider the following:
• Cost
• Access to critical data
For mission-critical applications, HP recommends that you implement a level 4, fully redundant
fabric configuration.
FICON SAN routing
This section describes FICON SAN routing. Several Fibre Channel routing features do not apply
to FICON SANs (for example, some fabric services are not used by FICON devices).
HP supports the following FICON SAN routing types:
• Single-director routing
• Cascaded-director routing
FICON SAN routing 23