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

SAN infrastructure
You use fabric switches to create the SAN communication paths. The number of storage systems
that can be connected is determined by the number of ports available and other hardware
constraints.
SANs enable expansion by scaling storage capacity across numerous systems and long distances.
Scaling increases the number of devices and connections in a SAN. You can increase the number
of switches in a fabric, or you can use routing technology to connect multiple SAN fabrics or
multiple VSANs.
Fabrics
A fabric is a single switch or a set of switches connected to form a network. Fabric services manage
device names and addresses, timestamps, and other functionality for the switches.
A set of switches can be connected as a single fabric, an interconnected network of independent
fabrics (LSANs for B-series), or partitioned into multiple logical fabrics (Virtual Fabrics for B-series
or VSANs for C-series).
SAN scaling
You can increase SAN connectivity by adding switches to an existing SAN or by using switches
with more ports. When designing a SAN, you must ensure compliance with Fibre Channel standards
and switch specifications. For switch-based scaling, consider the following factors:
• Fibre Channel architecture
Fibre Channel supports a maximum of 239 switches in a single fabric. HP specifies support
based on rules for the maximum number of switches and maximum number of ports in a single
fabric or multi-fabric SAN. Using many switches to obtain a high number of ports is
unacceptable if the fabric exceeds the total switch count limit. Likewise, using large-capacity
switches can create a network that exceeds the maximum number of ports.
For the HP-supported switch and port count fabric maximums, see:
◦ “B-series switches and fabric rules” (page 91)
◦ “C-series switches and fabric rules” (page 123)
◦ “H-series switches and fabric rules” (page 140)
• Supported configurations
Each Fibre Channel switch product line specifies the maximum number of ISLs, user ports, and
hop counts, as well as link distances and other configuration limitations. The supported
configurations determine the practical size of a SAN.
• Fabric services
Fabric services are distributed throughout the SAN to coordinate functions among all switches
in the fabric. A large SAN requires the management functions provided by high-end switches.
Some low-end switches have a limited capacity for expansion.
Routing technology facilitates SAN expansion beyond the capacity offered by switch-based scaling.
Fibre Channel switches
A switch is identified by its function in a SAN:
• Core (or director)—Provides ISLs for any-to-any connectivity
• Edge (or fabric or SAN)—Provides user ports for connecting servers and storage systems
For some switches, the model name (for example, HP StorageWorks Core Switch 2/64) indicates
its intended use in a SAN.
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