.Part 1 Architecture HP SAN Design Reference Guide 785351-001

performance and a higher number of available ports, since all fabrics can be accessed
simultaneously during normal operations.
Figure 13 Level 4: multiple fabrics and device paths (NSPOF)
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A B
Using two fabrics may increase implementation costs, but it also increases the total number of
available ports. For example, in a single meshed fabric with four switches, you have a maximum
of 52 user ports for servers and storage. Implementing the same topology using two fabrics increases
the maximum number of user ports to 104.
Considerations
When choosing a data availability level, you must consider:
• Cost
• Access to critical data
For mission-critical applications, HP recommends that you implement a level 4, fully redundant
fabric configuration. You can justify the additional cost if you consider the cost of losing access to
critical data.
Table 7 (page 40) indicates data availability and supported topologies for each level.
Table 7 Fabric design data availability
SAN topologiesAvailability levelFabric design
Single switch or multiple switches with single ISLNo redundancyLevel 1: single connectivity fabric
Cascaded with two ISLs, meshed, ring, and
core-edge
MediumLevel 2: single resilient fabric
AllHigh
Level 3: single resilient fabric with
multiple device paths
AllHighest
Level 4: multiple fabrics and device
paths (NSPOF)
You can add fabrics to increase the number of available ports. Table 8 (page 41) lists the cost
calculations for each data availability level.
40 SAN fabric topologies