The wall rack: nine devices in 8U, and three that aren't

Technical summary (AI generated)

• The doubt: fleet.json gave the wall rack 8U, yet twelve devices carried a position in it.
• The cause: rackOrder is a stacking order, not a rack-unit number; and three devices were never in the rack.
• The fix: NAS, UniFi access point and aria move to “not in a rack”; the remaining nine are renumbered 1 to 9 (labo#21).
• The result: nine devices in 8U, including two Pis in one 1U tray and four desktop boxes.
• Transparency: inventory reviewed in a session with Claude Code; the text and diagram were drafted with its help.

I’ve been saying “my wall rack, 8U” for a good while. One night, while re-reading the lab inventory with Claude Code, the nightly sync raised a flag: my inventory file gave the rack 8U, but twelve devices carried a position in it. Twelve devices in eight units doesn’t fit, however much goodwill you bring.

So I went back over it with Claude, device by device. The verdict is in the diagram below, but it fits in one sentence: I was right about the 8U, and wrong about the twelve.

A bit of context

The rack is an open two-post 8U frame bolted to the wall. It’s where the home network lives: the router, the switch, two nodes of my k3s cluster, the home automation, the phone and the UPS units. The lab inventory draws it automatically every night from a single file, and that file is what got caught out.

What was wrong, and what wasn’t

The rackOrder field fooled me too. I read it as a rack-unit number, when it’s only the order the devices are stacked in. That already explains part of the count: worker1 and worker2 share one 1U GeeekPi tray (the one from my July article), and the Netgate 1100, the Home Assistant Green, the Hilo gateway and the DP750 phone base are desktop boxes, not 19-inch gear. They don’t take a unit each, they share space.

The other part is that three devices simply weren’t in the rack. In full transparency, my inventory wrongly filed them in the rack:

• the NAS lives in an IKEA cube hung on the wall, left of the rack;
• the UniFi Wi-Fi access point is on the ground-floor ceiling;
• aria, a Raspberry Pi 4, is a spare put away somewhere since November 8.

Twelve minus three: nine. Claude fixed the file and the docs (labo#21, merged November 9), and I confirmed the answers one by one.

The diagram

Read top to bottom: a VCE patch panel, the GS348 switch, the two UPS units, a second patch panel, then the 1U Raspberry Pi tray. The tray has four slots: WORKER1 and WORKER2 are plugged in, and the other two are empty. Below, two shelves for the small boxes: the Hilo gateway on the upper one; on the lower one, the Netgate 1100 router (bottom left), the DP750 phone base and the Home Assistant Green.

The two patch panels aren’t inventory devices, which explains the rest of the count: six 19-inch units plus the two shelves make 8U.

In real life

The rack on November 12, 2026. The Home Assistant is on the lower shelf, on the right: that’s its antenna sticking out to the right of the rack.

And the same one, in July:

The July photo has aged: the tray holds three Raspberry Pis, including the one labelled COQUILLE, which is aria, my spare Pi 4. It has been put away since November 8 and is no longer in the tray. The Netgate 1100, the Home Assistant Green, the Hilo gateway and the DP750 are indeed in the rack, but they’re small boxes: you can barely make them out in the picture, hence the diagram.

The sequel: the ceiling access point

Taking the UniFi access point out of the rack surfaced something else. It’s on the ground-floor ceiling, powered over PoE by an injector, and the injector is not on a UPS (I found that in October, and it’s still the case). So at the first power cut, the Wi-Fi drops, and the camera that goes through it with it.

It’s a choice, not an oversight: the camera would lose its own power in a real outage anyway, and there’s no free battery outlet left on the two UPS units. But I’d never written it down anywhere, and that’s the kind of detail you rediscover at 2 a.m., in the dark.

Last word

An inventory that counts twelve devices in 8U was right to make me suspicious: a number that doesn’t fit its container is often a misread definition, not a wrong container.

— Ludo