Redundant Fabrics - HP StorageWorks 64 - SAN Director Switch Planning Manual

Fibre Channel fabrics are classified by four levels of resiliency and redundancy.
From least available to most available, the classification levels are:
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Redundant Fabrics

If high availability is important enough to require dual-connected servers and
storage, a dual-fabric solution is generally preferable to a dual-connected single
fabric. Dual fabrics maintain simplicity and reduce (by 50%) the size of fabric
routing tables, name server tables, updates, and Class F management traffic. In
addition, smaller fabrics are easier to analyze for performance, to fault isolate, and
to maintain.
SAN High Availability Planning Guide
Nonresilient single fabric — Directors and switches are connected to form a
single fabric that contains at least one single point of failure (fabric element or
ISL). Such a failure causes the fabric to fail and segment into two or more
smaller fabrics. A cascaded fabric topology
this design.
Resilient single fabric — Directors and switches are connected to form a
single fabric, but no single point of failure can cause the fabric to fail and
segment into two or more smaller fabrics. A ring fabric topology
on page 91) illustrates this design.
Nonresilient dual fabric — Half the directors and switches are connected to
form a one fabric, and the remaining half are connected to form an identical
but separate fabric. Servers and storage devices are connected to both fabrics.
Each fabric contains at least one single point of failure (fabric element or
ISL). All applications remain available, even if an entire fabric fails.
Resilient dual fabric — Half the directors and switches are connected to
form one fabric, and the remaining half are connected to form an identical but
separate fabric. Servers and storage devices are connected to both fabrics. No
single point of failure can cause either fabric to fail and segment. All
applications remain available, even if an entire fabric fails and elements in the
second fabric fail.
A dual-fabric resilient topology is generally the best design to meet
high-availability requirements. Another benefit of the design is the ability to
proactively take one fabric offline for maintenance without disrupting SAN
operations.
Planning Considerations for Fibre Channel Topologies
(Figure 36 on page 90) illustrates
(Figure 37
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