SAN Design: March 29, 2001 3:18 pm
53-0001575-01 BROCADE Technical Note Page: 17 of 31
Three Tier designs in general allow for higher port count fabrics over Star designs (using the same switch building blocks) but can add
additional hops to the design. A middle (core) set of switches can be used to provide connectivity between an upper and lower level of
switches. These designs are generally used when data traffic flows between devices attached to the top tier and devices on the bottom tier.
For example, hosts on the top tier and storage systems on the bottom. These kinds of connections will have minimal hop counts and also
multiple equal cost paths in the fabric to allow for load sharing. If devices at a given level need to communicate via the fabric, there may be
additional hops and less variety of paths for this communication. A sample of an acceptable tested three tier design is shown in Figure 10.
This particular design was used in Brocade’s Fabric Aware test program to validate heterogeneous device connectivity in a large SAN net-
work.
FIGURE 13. Three Tier Design used in Fabric Aware Testing at Brocade
There are a number of possible three tier designs that will work and that are generally in the 200 port count range. Shown in Figure 11 is
another example of an operating three tier design. This design includes an extended fabric link via DWDM allowing for connection of two
smaller SANs into a large SAN across a dark fiber link using DWDM equipment.
A1 A2 A8A3 A7A4 A5 A6 A9 A10 A11 A12 A13 A14
B1 B4
C1
B3B2
C2 C3 C4 C5 C6
Total of 268 ports available -- 196 host and 72 storage ports typical; total of 48 ISLs