Reply to post: Torus has its place, but there are downsides

You know what storage needs? More doughnuts to flatten us up

Steve Chalmers

Torus has its place, but there are downsides

The torus approach works best in fixed installations: imagine needing to add a few more devices to an existing, running torus. In the end, when we used even a basic ring back in the early days of Fibre Channel (Fibre Channel Arbitrated Loop, or FC-AL), the industry learned quickly that we needed to wire that loop in a star with wiring hubs to make adding/removing/failing/repairing devices straightforward. Even then, loop reconfiguration was disruptive enough that in the end low cost switching (the exact wiring needed for leaf-spine) won out.

The torus approach also needs to have the failure (immediate workaround, repair, return to normal) cases thought out well. A torus with hardware which forwards through a node in 80ns is doing so in hardware based on tables loaded into each ASIC by some sort of software control plane. There are a lot of "interesting" cases (black holes, forwarding loops, non simultaneous changes to forwarding tables by software, ...) beyond the basic operation described in this article.

Will be interesting to see where this torus design finds its home, and among what customers.

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