Minisforum UM790 Pro and UM890 Pro: The Quiet 2U Homelab Node

The UM790 Pro and the UM890 Pro occupy a specific slot in the homelab hierarchy: the machine you buy when a Raspberry Pi has run out of headroom, a used SFF desktop is more noise and more watts than you want in a closet, and a rack-mount server is frankly absurd for what you are running. Both are Zen 4 mobile silicon — eight cores, sixteen threads, a Radeon 780M riding along on the same die — packed into a chassis roughly 130 mm square and a touch under 50 mm tall. That is a legitimate eight-core node in a box about the size of a hardcover book.

The interesting part, and the reason they keep turning up in build threads, is that they are quiet. Not "quiet for a server" quiet — actually quiet, the kind of quiet where you have to look at the fan graph to confirm the thing is under load. That property is easy to destroy with a bad mount. The cooling design on both of these machines depends on unobstructed intake and a clear exhaust path, and a rack is a hostile environment for both. This post covers what you are actually mounting, why it lands at 2U and not 1U, and how to keep the quiet you paid for.

The mount for this build:

10" Minisforum UM790 Pro Mini PC Rack Mount - 2U

What you are actually racking

The two machines are close enough that most of this post treats them as one device, which is deliberate — but they are not identical, and the differences matter for a couple of decisions downstream.

The UM790 Pro runs a Ryzen 9 7940HS: Zen 4, eight cores, sixteen threads, with the 780M integrated graphics. The UM890 Pro moves to the 8945HS, which is the same core architecture with a higher clock ceiling and the XDNA NPU bolted on. For a homelab running Proxmox, a handful of LXC containers, and maybe a media transcode now and then, the practical performance gap between them is small. The NPU is not doing anything for you unless you are deliberately feeding it, and most people are not.

Both take two DDR5 SODIMMs and both have M.2 2280 NVMe capacity — the UM890 Pro is the more generous of the two on storage slots, which is the real reason to pick it if you are building a node that needs a boot drive plus a data drive without going external. Both carry USB4 on the front, which turns out to have rack implications that nobody thinks about until the cables are in. More on that below.

Physically, they share a family shell. The footprint is close to square, a bit over 125 mm on a side, and the height sits under 50 mm before you count the rubber feet. That last number is the one people latch onto, and it is the source of the most common question about these machines.

Why these are 2U and not 1U

A rack unit is 44.45 mm under EIA-310-D. The UM790 Pro and UM890 Pro chassis, without feet, are taller than that — but not by much. So the arithmetic looks tantalizing, and roughly once a month someone asks whether a 1U version exists.

It does not, and it should not. There are three problems with the 1U idea, and each one alone is disqualifying:

• The device is already over 1U. Not marginally under, like some mini PCs — over. There is no amount of clever mounting that compresses 48 mm into 44.45 mm.
• The intake is on the bottom. Both machines pull the majority of their air through a perforated underside. A 1U design would have to press the chassis against a structural plate to save height, which is the one thing you must not do.
• The mount needs material. A front face that resists flex, side rails that hold the device square, and a floor with enough thickness not to sag under a kilogram of aluminum all consume vertical space.

Two rack units is 88.9 mm. That leaves roughly 40 mm of slack above and below the chassis once the mount is accounted for, and that slack is not wasted — it is the plenum that keeps the fan curve flat. The 10" Minisforum UM890 Pro Mini PC Rack Mount - 2U uses that clearance deliberately: open underside, open rear, and a front face that holds the machine without wrapping it.

The thermal story, and where the quiet goes

The 7940HS and 8945HS are nominally 45 W parts with configurable TDP, and Minisforum runs them above the floor. Under a sustained all-core load, expect the package to settle somewhere in the 50 to 65 W neighborhood. The cooler is a vapor chamber feeding a small blower, and on some UM790 Pro production runs Minisforum used liquid metal between die and cold plate rather than paste — which is part of why these run as cool as they do, and also a reason not to open one casually.

Here is the behavior that matters in a rack. At idle and light load, the blower sits at a low, essentially inaudible RPM. The fan curve is flat across a wide band and then climbs fast once the package hits its thermal target. That means the difference between "silent" and "audible whine" is not a load threshold — it is a temperature threshold, and you control the temperature side of that equation with airflow.

Restrict the bottom intake and the package hits its target sooner, so the blower spends more of its life in the steep part of the curve. You do not lose performance in any dramatic way; these machines do not throttle hard in normal homelab use. You lose the silence. People mount one of these on a solid shelf, hear a fan they never heard on the desk, and conclude the unit is defective. It is not defective, it is breathing through a plate.

The practical rules are short: leave the underside open, keep the rear clear of cable bundles, and do not stack a heat source directly beneath it. A PoE switch running twenty watts of budget underneath a UM890 Pro will raise the intake temperature by a few degrees, which is enough to move the fan into the audible band on a warm afternoon.

Power, UPS sizing, and closet heat load

Both machines ship with an external brick in the 120 W class. Do not size anything off that number. The brick is rated for transient peaks plus a healthy margin, and the actual draw is nowhere near it.

A realistic profile for a homelab node running a hypervisor with a modest container load: high single digits to mid teens of watts at idle, somewhere in the 20 to 35 W range at typical mixed load, and 80 to 95 W only during a sustained all-core benchmark that your actual workload probably never produces. If you are sizing a UPS, plan around the mixed-load number with headroom, not the brick rating. A 1500 VA unit that would carry a single tower will carry three of these plus a gateway and a switch with runtime left over.

For closet heat-load math, the conversion is 3.412 BTU/hr per watt. A node sitting at 30 W is contributing roughly 100 BTU/hr. Two of them plus a gateway and a PoE switch lands you somewhere near 500 BTU/hr, which a small enclosed closet will notice over the course of a summer afternoon and an open rack will not. Worth doing the arithmetic before you build the closet, not after.

One brick note: the power connector is on the rear, and the cable is stiff. If you are mounting in a shallow 10-inch cabinet, measure the depth you have behind the rails before you commit. The 19" Minisforum UM790 Pro Mini PC Rack Mount - 2U (Modular) gives you more room to route that cable cleanly, which is a real consideration if depth is tight.

Ten-inch or nineteen-inch: picking the mount

The device is the same either way; the question is what rack it is going into and what else is going in beside it.

In a 10-inch mini rack, the machine takes essentially the full usable width. You get one node per 2U and that is the whole story. This is the right answer for a network closet or a shelf-mounted cabinet where the rack exists to hold a gateway, a switch, a patch panel, and one or two compute nodes. The dedicated 10-inch mounts are the simplest path here.

In a 19-inch rack, one of these machines occupying a full 2U by itself is a waste of about two-thirds of the width. That is what the modular mounts solve — a shared 19-inch face with device-specific carriers, so you can put a UM890 Pro next to another device at the same height. If you are running a pair of nodes for a Proxmox cluster, the 19" Minisforum UM890 Pro Mini PC Rack Mount - 2U (Modular) gets both of them into a single 2U slot instead of burning 4U on two mostly-empty faces.

A three-node cluster is where this gets genuinely worth planning. Three of these in dedicated full-width 19-inch mounts is 6U. Three in modular carriers, if your width allows, is considerably less — and the cabling story improves at the same time, because the rear exits line up in one horizontal band instead of three.

The USB4 cabling gotcha

Both machines put USB4 on the front panel, which is excellent on a desk and mildly annoying in a rack. If you are using USB4 for anything persistent — an external NVMe enclosure, a dock, a capture device — that cable now lives on the front of your rack, where it crosses the face of whatever you mounted above and below.

There is no elegant fix, only choices. Either you accept a front-facing cable and route it neatly down one side of the rack, or you move the peripheral to a rear USB port and give up USB4 bandwidth, or you do not use USB4 in the rack at all and keep those ports for maintenance. Most people end up at option three without deciding to, which is fine — just know that the "I will run my storage over USB4" plan has a cosmetic cost in a rack that it does not have on a desk.

The related point: leave yourself front access. A mount that buries the front panel makes reseating a display cable or plugging in a keyboard for a BIOS trip into a rack-disassembly job. The front face on these mounts is cut to keep the ports reachable for exactly that reason.

Wrap-up

The UM790 Pro and UM890 Pro rack well, and the criteria for doing it right are narrow enough to list. Give them 2U, because the chassis is already taller than a rack unit and the math does not bend. Keep the underside open, because that is where the air comes from and blocking it is how you turn a silent machine into an audible one. Keep the rear clear of cable bundles. Size your UPS off roughly 25 to 30 W of real draw rather than the 120 W brick, and budget about 100 BTU/hr per node if you are doing closet heat-load arithmetic. Pick the 10-inch mount for a mini rack where the node gets the full width anyway, and the modular 19-inch carrier when you are pairing nodes and want to stop wasting width. Get those right and the machine behaves in a rack exactly the way it behaved on your desk, which is the entire point.

Mounts in this build