Figure 2-8 shows an example of traffic segregation on the SAN using edge-core-edge  topology. Even when sharing the same core switches, it is possible to use virtual switches (see 2.2.7,  “SAN partitioning” for details) to isolate one tier  from the other. This configuration helps avoid  traffic congestion caused by slow drain devices that are connected to the backup tier switch. SAN partitioning is a hardware-level feature that allows SAN switches to share hardware  resources by partitioning its hardware into different and isolated virtual switches. Both  Brocade and Cisco provide SAN partitioning features called, respectively,  Virtual Fabric  and  Virtual SAN  (VSAN). Hardware-level fabric isolation is accomplished through the concept of switch virtualization,  which allows you to partition physical switch ports into one or more “virtual switches.” Virtual  switches are then connected to form virtual fabrics.  As the number of available ports on a switch continues to grow, partitioning switches allow  storage administrators to take advantage of high port density switches by dividing physical  switches into different virtual switches. From a device perspective, SAN partitioning is  completely transparent and so the same guidelines and practices that apply to physical  switches apply also to the virtual ones. 2.2.7 SAN partitioning Figure 2-8 Segregation using edge-core-edge Chapter 2. Storage area network  21