FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availability Planning Guide (AA-RS2DC-TE, June 2003)

Planning Considerations for Fibre Channel Topologies
90 SAN High Availability Planning Guide
Figure 36: Cascaded fabric
One design variation is to use more than one ISL between fabric elements. This
eliminates ISLs as a single point of failure and greatly increases the fabric design
reliability.
Cascaded fabrics are well suited for applications where data access is local, but
not for applications that require any-to-any connectivity. Device locality implies
that groups of servers and the storage they access are connected through the same
fabric element, and that ISLs are used primarily for fabric management traffic
(Class F traffic) or low-bandwidth SAN applications. For additional information,
refer to “Device Locality” on page 100.
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