February 2021 — on the noise that comes from spinning rust and how to stop it from travelling

Every NAS build guide covers the same things: which board, which drives, which OS, how many watts. They cover RAID levels, ZFS recordsizes, network throughput. They benchmark transfer speeds and idle power.

Almost none of them talk seriously about vibration isolation. This is a mistake, because in a home environment, the vibration is often the only thing you actually notice day to day.

The problem with hard drives in an enclosure

A spinning hard drive vibrates. The platters spin at 5400 or 7200 RPM, the heads actuate, and the whole assembly resonates at frequencies that depend on the drive model, firmware, and workload. Individually, the vibration is modest. In an enclosure with four, six, or eight drives, the vibration couples through the metal chassis and the drives can excite each other — a phenomenon called acoustic coupling that increases seek time errors and accelerates wear.

The enclosure also acts as a resonator. A metal case with drives bolted directly to it transmits vibration efficiently to whatever surface it sits on. Sit it on a wooden shelf and the shelf becomes a speaker membrane. The result is a NAS that is perceptibly present in the room even when it’s doing nothing interesting.

The fix is to break the transmission path. You need compliance between the drive and the chassis — something that absorbs the vibration before it reaches the metal.

The case

The Fractal Node 304 (or similar compact ITX NAS enclosure) is a good starting point: compact, designed for 3.5" drives, reasonable airflow. The stock drive mounting uses hard metal screws into the drive mounting frames. This works mechanically. It transmits every Hz the drives produce directly into the chassis.

The enclosure comes with rubber-grommet mounting positions on some of the bays — use them. Where it doesn’t, the modification is simple: apply silicone sealant to the contact points between the drive and the mounting frame.

The silicone approach

Silicone sealant — standard neutral-cure silicone, the kind used for bathroom sealing — applied in a controlled bead pattern between the drive and its mounting frame provides compliance without rigidity. The silicone cures to a rubber-like material that absorbs vibration across a wide frequency range.

The technique:

1. Clean the drive mounting frame and the drive sides with isopropyl alcohol
2. Apply silicone in a snaking bead pattern across the frame surface that contacts the drive
3. Press the drive in place and allow to cure fully before powering on (24 hours minimum)
4. The silicone holds the drive in position mechanically while providing acoustic isolation

The bead pattern matters — you want coverage across the contact surface without gaps (which allow metal-to-metal contact at those points) and without so much material that the drive can’t seat correctly.

The result

The difference between hard-mounted drives and silicone-isolated drives in the same enclosure is audible. Not subtle — the characteristic hard-drive seek noise and low-frequency resonance that transmit through the chassis are significantly reduced. The NAS is not silent; spinning drives make noise. But the noise stays inside the enclosure rather than becoming the room’s ambient sound.

The shelf doesn’t hum. The floor doesn’t hum. The NAS sits in the network cupboard and is not noticed.

For a device that runs 24/7, this matters more than the difference between 350 MB/s and 380 MB/s sequential throughput.

The rest of the build

The NAS runs TrueNAS Scale. Four drives in a mirrored vdev — not the most space-efficient configuration but the simplest to reason about for recovery. ZFS handles checksumming, compression (lz4 on most datasets), and weekly scrubs.

Power consumption at idle: low enough to not care about. The drives spin down after inactivity. The CPU idles efficiently enough that the power bill is not the point of this exercise.

The network is a direct 1GbE connection to the home switch — enough for the workload, not interesting enough to write about. The services running on top are more interesting: Immich for photo management, Time Machine targets for the Macs, a general SMB share for everything else.

The drives are the least interesting part of a NAS. The discipline of backups, the choice of filesystem, the monitoring setup — those matter. The vibration isolation is the one physical thing that affects daily quality of life, and it’s the one thing that costs €2 of silicone and an afternoon.

Do it before you close the case.