From 1f7db6d4b086da9775c9ee7b0155d7b7c4b15190 Mon Sep 17 00:00:00 2001 From: Zeb Hering Date: Fri, 28 Aug 2026 23:05:58 -0700 Subject: [PATCH] Document matching Dell on CPU rather than out-bidding it With the service stopped under sustained load, Dell held 5880-6120 RPM with CPU2 at 70-74c. The CPU ramp calibrated from an idle reading asked for 36-50% over that same range - up to 9720 RPM - while the drives ran 2c warmer. The extra airflow bought nothing. Dell has the chassis thermal model and does CPU cooling well; what it cannot see is drive temperature. Keeping the CPU ramp out of the way until 75c and reaching full at 77c (iDRAC's own warning point) matches stock RPM for 50 of 60 samples under load. Co-Authored-By: Claude Opus 5 (1M context) --- README.md | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/README.md b/README.md index fca70a7..d4ad963 100644 --- a/README.md +++ b/README.md @@ -189,6 +189,25 @@ The rule: find the drives' normal peak, put `DISK_RAMP_LOW_OFFSET` a couple of d 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. +### Let Dell do the CPU; the disks are what it cannot see + +Dell's profile has the chassis thermal model and is good at CPU cooling. What it does not +do is look at drive temperature *at all*. So the CPU curve should approximate Dell's +rather than out-bid it, and the disk curve is where this script earns its keep. + +Measured on `iz-pve0` under a sustained migration, with the service stopped so Dell had +control: Dell held **5880-6120 RPM with CPU2 at 70-74c** — 3c below its own 77c warning +point. An earlier CPU ramp of 62-73c asked for 36-50% across that same range, i.e. up to +**9720 RPM against Dell's 5880**, while the drives ran 2c *warmer*. The extra 3800 RPM +bought nothing. + +The fix was to keep the CPU ramp out of the way until 75c and reach full speed exactly at +77c, where iDRAC itself starts warning. Result: 26% / 5880 RPM for 50 of 60 samples, +matching stock, with brief excursions to 35% when CPU2 touched 76c. + +Calibrating the CPU ramp against an *idle* reading is what caused this. Idle tells you +where the floor should be; only a loaded CPU tells you where the ramp should start. + ### 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.