HP StorageWorks 4000/6000/8000 .HP StorageWorks SAN Design Reference Guide, Pa - Page 30

against hardware failure, high-availability topologies connect redundant systems. You can connect a complex and extensible network across long distances by choosing the required topology and appropriate components, and then connecting devices with fiber optic cable. 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 "H-series switches and fabric rules" on page 83, "B-series switches and fabric rules" on page 93, "C-series Fibre Channel and FCoE switches and fabric rules" on page 135, and "M-series switches and fabric rules" on page 157. • 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. 30 SAN design overview