Stage count - is number of devices I need to pass through in order to get from source to the destination.

Clos fabric is a non-planar graph - there is no way to draw all those connections on a flat plane without crossings.

5-stage fabrics type:

• Fat tree
• Benes
• Butterfly

Over-subscription - is the ratio between total bandwidth offered to workloads and to total available fabric bandwidth.

Total Edge port count = spine ports * over-subscription * break-out ration.

Example 1 - three stage Clos using 64×100 spines and leafs with over-subscription 2:1 can provide 4096 edge ports.

Example 2 - 5 stage butterfly using 64×100 fabrics with over-subscription 2:1 can provide 65536 edge ports.

It's possible to add 7th stage, which often used for DCI.