I’ve been using fans bigger than 80mm in desktop machines for a long time. Is there a reason to prefer 2U1N over the equally dense 4U2N shape? Obviously 2U is widely available and 4U dual node is exotic, but I imagine that Cloudflare has plenty of scale for a custom form factor if it would benefit them.

Seems to be right, but as far as I can tell almost nobody uses this terminology and it's pretty rude of the article not to explain.

Like, this article is one of the top results for 2U1N, plus some dell pages and random jank.