99f9bf8d89
Power/temp sweep (2026-06-05) located the cooling-per-watt knee at ~60%: 60->70% buys only -2C for +21W, and 70->100% buys 0C for +54W (the CPU floors ~59C at cluster load, so more airflow does nothing). Re-tune the COOL curve to cap its normal band at 60% (~303W, ~61C); 80/100% become a high-load safety ramp (>=73/79C) before the 83C ceiling. QUIET unchanged (already at the 281W / 4800rpm floor). Saves up to ~75W (~650 kWh/yr) vs full-tilt for the last ~2C. Tests + design doc updated; verified live (63C, 60%, ~267W). [ci skip] Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
117 lines
5.2 KiB
Markdown
117 lines
5.2 KiB
Markdown
# PVE R730 presence-aware fan control — design
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**Date:** 2026-06-04
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**Status:** implemented
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**Scripts:** `infra/scripts/fan-control.{sh,service,env.example}`, `test-fan-control.sh`
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**Runbook:** `infra/docs/runbooks/fan-control.md`
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## Problem
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The Dell R730 PVE host (192.168.1.127) runs its CPU at ~72–77°C under normal
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cluster load. That is safe (firmware warning at 88°C, critical 93°C) but the
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iDRAC's stock fan curve optimises for quiet, not cool — it pins the fans at the
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~7080 RPM floor even at 72°C / load 30 and only ramps near ~80°C. We want the
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CPU to run cooler when it costs nothing (the box is in the garage, usually
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empty) while staying quiet when someone is physically in the garage.
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## Measured fan/temp relationship (manual IPMI sweep, 2026-06-04)
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At a comparable CPU load (~45–53 % busy):
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| Fan setting | Fan RPM | CPU temp |
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|-------------|---------|----------|
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| Auto (floor) | 7,080 | 71–72°C |
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| 50 % | 9,360 | 65–66°C |
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| 70 % | 12,800 | 60–61°C |
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| 100 % | 17,000 | 55–56°C |
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Best °C-per-RPM is the first step; beyond ~70 % it is mostly noise. ~16°C of
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swing is available.
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## Power characterization (sweep 2026-06-05)
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Averaged wall power (iDRAC DCMI) + temp at each fan setting:
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| Fan | RPM | Power | CPU | load |
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|-----|-----|-------|-----|------|
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| auto | 7,080 | 296 W | 68°C | 21 |
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| 20 % | 4,800 | 281 W | 73°C | 20 |
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| 30 % | 6,360 | 288 W | 72°C | 19 |
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| 50 % | 9,360 | 299 W | 65°C | 18 |
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| 60 % | 11,040 | 303 W | 61°C | 17 |
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| 70 % | 12,720 | 324 W | 59°C | 16 |
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| 100 % | 16,920 | 378 W | 59°C | 17 |
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**The cooling-per-watt knee is ~60 %.** Fan power follows ~RPM³: 60→70 % costs
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+21 W for −2°C; 70→100 % costs **+54 W for 0°C** (the CPU floors ~59°C at cluster
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load — more airflow does nothing). Full speed draws ~97 W (~850 kWh/yr) over the
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floor and buys nothing past 60 %.
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**Decision (2026-06-05):** the COOL curve caps its normal band at 60 % (~303 W,
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~61°C) — capturing essentially all achievable cooling while avoiding the wasteful
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80–100 % zone, now reserved as a high-load safety ramp (≥73/79°C) before the 83°C
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ceiling. QUIET is unchanged (already at the low-power floor: 20 % / 4,800 RPM /
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281 W). Verified live after re-tune: 63°C, 60 %, ~267 W.
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## Decisions
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1. **Custom bash daemon + systemd service**, deployed to the PVE host the same
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way as `apply-mbps-caps` / `daily-backup` (source in `infra/scripts/`, scp to
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`/usr/local/bin`). It cannot be Terraform/k8s — it runs on the bare host where
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IPMI lives. (OSS `tigerblue77/Dell-iDRAC-fan-controller` was considered;
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rejected — it is a Docker container, off-pattern here, and unaware of our
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constraints.)
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2. **CPU temperature is the only control input.** The Tesla T4 has its own
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always-on fan (owner-confirmed), so it self-cools and does not depend on
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chassis airflow — no GPU coupling needed.
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3. **Presence = the garage door**, because the server is *in the garage*
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(memory id=1723); noise only matters to people physically there. Signal:
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ha-sofia `sensor.garage_door_state_bg`. Open now, or last changed within
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`HOLD_SECS` (15 min) ⇒ someone's around ⇒ QUIET; otherwise COOL.
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`house_mode` was rejected — it tracks *apartment* occupancy, irrelevant to
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garage noise.
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4. **Two curves**, picked by presence (COOL power-tuned 2026-06-05 — see
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"Power characterization" below):
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| CPU °C | COOL % (empty) | CPU °C | QUIET % (occupied) |
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|--------|----------------|--------|--------------------|
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| ≤54 | 30 | ≤72 | 20 (≈silent floor) |
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| 55–63 | 50 | 73–77 | 40 |
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| 64–72 | 60 (knee) | 78–81 | 65 |
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| 73–78 | 80 | ≥82 | 100 |
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| ≥79 | 100 | | |
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3°C downward hysteresis prevents flapping at band edges (ramp up immediately,
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step down only once the curve still wants lower 3°C hotter).
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## Safety
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Manual fan mode bypasses the iDRAC's own protection, so it is backstopped:
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- **Daemon exit/crash/stop** → bash `EXIT` trap + systemd `ExecStopPost` both
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run `ipmitool raw 0x30 0x30 0x01 0x01` (restore Dell auto). `Restart=on-failure`.
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- **CPU ≥ `CEILING` (83°C)** → hand back to Dell auto until temp holds below
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`RESUME_BELOW` (75°C) for `RESUME_STABLE` (120 s), then resume manual.
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- **IPMI read failures ≥ `MAX_IPMI_FAILS`** → restore Dell auto.
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- **ha-sofia unreachable** → keep the last good presence decision; default COOL
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at cold start (thermally safe).
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## Observability
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Pushes to the existing Pushgateway (`http://10.0.20.100:30091`, job
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`fan_control`): `pve_fan_control_cpu_temp_celsius`, `_fan_percent`, `_mode`
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(1 quiet / 2 cool / 0 fallback), `_ha_reachable`, `_fallback`. The existing CPU-
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temp alert is unaffected.
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## Testing
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`test-fan-control.sh` sources the script (main is guarded by a `BASH_SOURCE`
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check) and unit-tests the pure functions: both curves, hysteresis up/down,
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presence open/recent/stale, temperature parsing, jq-free JSON field extraction,
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and percent→hex. 36 assertions, no hardware needed. The daemon also supports
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`DRY_RUN=1` and `RUN_ONCE=1` for integration checks.
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## Rollback
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`systemctl disable --now fan-control && ipmitool raw 0x30 0x30 0x01 0x01` on the
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host returns the box to stock firmware fan control. See the runbook.
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