Count top-of-rack switches for a row from server NIC ports, uplink reservations and dual-ToR redundancy.
Server ports are the product of servers and NIC ports per server, and only the ports not reserved for fabric uplinks can terminate them. Dual-ToR halves the load on each plane but doubles the switch count, because each plane must be able to carry the rack alone. Switch count drives licence, optics and power budgets, and forgetting the uplink reservation is how a 48-port switch turns out to hold only 42 servers.
Top-of-Rack Switch
usable ports = ports per switch − uplink reservations; switches per rack = ceil(server ports ÷ planes ÷ usable ports) × planes.
usable ports = ports per switch − uplink reservations; switches per rack = ceil(server ports ÷ planes ÷ usable ports) × planes. Server ports are the product of servers and NIC ports per server, and only the ports not reserved for fabric uplinks can terminate them. Dual-ToR halves the load on each plane but doubles the switch count, because each plane must be able to carry the rack alone.
Switch count drives licence, optics and power budgets, and forgetting the uplink reservation is how a 48-port switch turns out to hold only 42 servers.
This calculator takes 6 inputs: Racks, Servers per rack, Data NIC ports per server, Ports per switch, Ports reserved for uplinks, Dual-ToR (split NICs across two planes). The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.