THE COMPUTE DESK

02 / THE CLUSTER

From racks to a cluster

A rack holds the computers. A network joins racks so a workload can use them together. This simplified row shows where the switches and connections sit.

Compute racks

Servers and GPUs perform the work.

Leaf switches

Local switches collect traffic from the racks.

Spine switches

Shared switches connect those local groups.

Stage I — the row · front elevation overhead tray — schematic inter-rack cable assemblies one possible leaf placement rack 3 — the NVL72 from the rack page spines 8 compute racks · row ≈ 6 m

A still view of the room. The interactive model is unavailable, but the four chapters still explain how it works.

One representative layout, not a construction drawing. Lines show logical connections; a real connection may need several lanes or cable assemblies. In the rail view, each long line groups many point-to-point links—it is not one shared physical cable.

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Physical layout assumptions & sources
Decision supported
Does the physical layout match the quoted logical fabric?
Primary output
Placement, cabling, and failure-domain diligence
Evidence boundary
Representative row, not a construction drawing or cable schedule

Physical-design diligence

The topology diagram becomes a placement and port map. A supplier's logical leaf and spine tiers must resolve to physical switches, ports, cable assemblies, and pathways. This illustration places leaves at top of rack and spines at end of row; other designs use middle-of-row, centralized, or distributed placement. Ask for both diagrams and reconcile them.

Distance and line rate determine media. Short links may use passive copper; longer or faster links may require AEC, AOC, or optical assemblies. A logical edge may map to multiple lanes or cables, and the cost depends on the actual bill of materials. At 2:1, this illustration removes half the leaf-to-spine capacity; an actual assembly count requires a port map. Model the communication sensitivity →

Rails change both cost and failure shape. In the single-plane illustration, removing a rail switch affects the corresponding path across attached nodes. Redundant planes, routing, and collective configuration determine whether jobs stall or continue at reduced bandwidth. Configure the topology estimate →

Ask the supplierWalk me down the row: which rack holds the spines, how many fibers are in the tray at my oversubscription ratio — and when one rail switch dies, which port goes dark on which racks, and which of my jobs stall?

This model keeps the wiring readable: eight racks, four spines, and one drawn line per logical uplink. It does not size network interfaces, lanes, cable assemblies, cooling, or power. Treat the room as a way to trace connections before reviewing the actual design.

schematic representative row · logical edges are not a construction cable schedule · model version 2026.08 · methods & limitations