From 02cd1a400413f28b8c8418d50c0fb75536563ac9 Mon Sep 17 00:00:00 2001 From: Zeb Hering Date: Fri, 28 Aug 2026 21:37:51 -0700 Subject: [PATCH] Document putting the disk ramp above normal working temperature A ramp that starts inside the range drives normally occupy makes every load spike move the fans, which cycles audibly. On iz-pve0 the rpool mirror works at 53-61c against a ramp starting at 52c, holding the fans at 7920 RPM (+27% over stock) to cool drives rated to 70c. Starting the ramp at 62c holds stock RPM flat and the drives settle at 53-54c. Co-Authored-By: Claude Opus 5 (1M context) --- README.md | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/README.md b/README.md index 6d5d894..ba84f61 100644 --- a/README.md +++ b/README.md @@ -111,6 +111,23 @@ holds 6240 RPM. Here 28% PWM == 6240 RPM, so `LOW_FAN_SPEED=28` and `CPU_RAMP_LOW_OFFSET=15` (ramp starts at 62c). An R730xd (`iz-pve1`) idling at 48c is fine on the 18/24 defaults. Put the values in the unit as `Environment=` lines. +### Put the disk ramp above the drives' normal working temperature + +The single most common cause of a noisy host is a disk ramp that starts *inside* the +range the drives normally live in. Then every load spike pushes the fan up, the fan drops +back, and it cycles audibly forever. + +Worked example, `iz-pve0`: `sda`/`sdh` are the rpool mirror in rear bays — busy root SSDs +that idle at 53-55c and touch 60-61c under load, rated to 70c. With the default ramp +starting at 52c they were permanently part-way up it, dragging the fans to 7920 RPM +(+27% over stock) to cool drives that were never in trouble. Starting the ramp at 60c +still cycled, because load spikes crossed it. Starting it at **62c**, just above their +working peak, holds 6240 RPM flat — and the drives settle at 53-54c anyway. + +The rule: find the drives' normal peak, put `DISK_RAMP_LOW_OFFSET` a couple of degrees +above it, and let the alarm (`DISK_ALARM_OFFSET`, 5c below the limit) catch anything real. +Cooling a healthy drive from 57c to 53c is not worth 27% more fan. + ### Expect to run above stock on some hosts, legitimately Dell's profile does not look at drive temperature at all — only CPU, inlet and exhaust.