Q-Logic 16HA user manual Cascade Bandwidth, Cascade Physical Distance between Chassis

Cascade Topology

Cascade Bandwidth

A chassis in a Cascaded topology divides its chassis interconnection bandwidth between adjacent chassis. That is, half of the T_Ports connect one direction around the loop and the other half connect the other direction around the loop. Even if you cable half of the chassis ports to T_Ports, you will only have one quarter of the chassis bandwidth connected in the direction of the least number of chassis hops to the destination chassis. Each Chassis will route traffic in the direction of the least number of chassis hops to the destination chassis. A chassis will route traffic in the other direction only if all links in the closest direction fail.

Also, traffic destined for any port NOT on the same chassis as the source port will be sharing the interconnection bandwidth with any other ports on other chassis that need to communicate over those same chassis links.

In fabrics of two or three chassis, Mesh and Cascade-with-a loop topologies are the same for purposes of bandwidth. For fabrics of four or more chassis, Mesh topology must use only one T_Port connected to each other chassis in the fabric because if you used two or more from each chassis you would use up too many ports to interconnect the chassis. Thus, cascaded connections may result in better bandwidth than Mesh.

Multistage topology has the best bandwidth. All T_Ports from each IO/T chassis connect (through the CC chassis) to all other IO/T chassis in the same number of chassis hops (three) no matter how large the fabric is. Thus the useful interconnec- tion bandwidth from each IO/T chassis increases by 100MBs per T_Port. It is possible in Multistage topology to devote half of the chassis bandwidth to T_Ports thus providing as much as 800 MBytes per second bandwidth between any two IO/T chassis.

Cascade Physical Distance between Chassis

Cascade topology can cover the largest campus area relative to other topologies. A cascaded topology can be laid out in a loop with the distance between adjacent chassis equal to or less than the maximum cable length of the installed GBICs.

SANbox-16HA Fibre Channel Switch		Multi-Chassis Fabrics 5-7
Installer’s/User’s Manual	59005-03 Rev. A