Designing and sizing an Al cluster with SkyD by Upscale

Designing and sizing an Al cluster with SkyD by Upscale. Nicolas Fevrier introduces SkyD (Sky Design), a new tool built by Upscale AI, to address the inherent difficulties in designing and sizing AI clusters. The complexity arises not from the concept itself, but from the immense scale of elements involved, such as thousands of GPUs, hundreds of switches, and thousands of cables and fibers, which become impossible to manage manually. The tool was initially developed to create illustrations and design topologies for Upscale’s internal validated designs, evolving to encompass broader functionalities for comprehensive cluster planning.

SkyD facilitates the design process by focusing on the fundamental components: the ports on compute servers (like Nvidia B300 or GB300 systems) and the characteristics of the network switches. It applies a series of constraints and rules to derive precise sizing for the backend, frontend, and management networks. The tool also helps anticipate potential failures, considering how to prepare for switch, optic, or fiber outages, and translates abstract claw designs (leaf-spine, superspine) into practical, real-world site maps. Key considerations include avoiding oversubscription on the backend network while allowing it on the frontend, and leveraging multiple network planes to enhance redundancy and significantly expand the number of GPUs supported within a two-tier network.

Beyond logical network design, SkyD extends to the physical world, enabling users to optimize fiber distances and simplify deployment. It generates floor maps, organizes racks, and defines rack elevations, providing detailed visualizations and optimizing cable routing to reduce overall fiber lengths. The tool includes a resiliency map that calculates the impact of potential outages on bandwidth, helping users plan for fault tolerance. Nicolas Fevrier announced that SkyD will be publicly available on upscale.com very soon, requiring a one-time registration, and will be continuously improved. It serves as a crucial “Day minus one” tool for architects preparing Upscale’s validated designs.