Hello,

Thank you for the detailed question. This is a common concern when upgrading CPUs in the PowerEdge R740, and it is good that you are thinking about thermal and acoustic implications before making the change.

To address your main question directly, the fan behavior on the R740 is primarily driven by thermal demand rather than purely by the TDP rating of the installed processors. The iDRAC thermal management system monitors actual CPU temperatures, inlet air temperature, and other component temperatures in real time, and adjusts fan speeds accordingly. This means that a 150W processor at idle will not necessarily cause the fans to spin dramatically faster than a 125W processor at idle, because at idle both CPUs will be drawing well below their rated TDP and producing relatively similar amounts of heat. The TDP rating represents the maximum sustained thermal output under full load, not the power draw at idle or light workloads.

That said, there are some important nuances to consider.

Since you mentioned your workload is bursty with the CPUs being idle most of the time, the 6240 at 150W should behave quite similarly to the 6230 at 125W during those idle periods. Both processors are based on the same Cascade Lake architecture and will have comparable idle power draw. The difference will become apparent during burst activity, where the 6240 will draw more power and generate more heat, prompting the fans to ramp up more aggressively. However, since these are bursts rather than sustained loads, the fans should ramp back down once the burst completes and temperatures settle.

Regarding the heatsink requirement, you are correct that the 6240 at 150W will require the high-performance heatsinks. This is important because the high-performance heatsinks have greater thermal dissipation capacity, which actually helps keep temperatures lower and can reduce the need for aggressive fan speeds. If you were to install the 6240 with standard heatsinks, the system would detect a thermal configuration mismatch and would likely run the fans at elevated speeds constantly to compensate, which would create exactly the jet engine scenario you want to avoid. So make sure you obtain the correct high-performance heatsinks (Dell part numbers for the R740 high-performance heatsinks can be confirmed through Dell's parts catalog or by contacting Dell Sales) before performing the upgrade.

Regarding the SoundCap profile you are currently using, this thermal profile is specifically designed to cap fan speeds at a lower maximum to reduce noise. It does this by limiting the maximum fan speed the system will use, which is generally fine for moderate workloads but can result in thermal throttling if the CPUs are under sustained heavy load and the capped fan speed is insufficient to cool them. With the 6230 at 125W, the SoundCap profile should continue to work well, much as it does with your current Silver 4110 processors. With the 6240 at 150W, the SoundCap profile will still function, but you may be more likely to encounter thermal throttling during prolonged burst activity because the fans will be capped and may not be able to dissipate the additional heat quickly enough. For bursty workloads with long idle periods in between, this may not be a practical issue, but it is worth being aware of.

If keeping noise levels as low as possible is a high priority and your workloads are truly bursty rather than sustained, the 6230 at 125W is the safer choice from an acoustic standpoint. You can keep the standard heatsinks, continue using the SoundCap profile without concern, and still gain a significant performance uplift over the Silver 4110. The 6240 will give you somewhat higher clock speeds and the same core count, but the trade-off is the need for high-performance heatsinks and slightly more fan activity during burst periods.

One additional item to note is that when upgrading CPUs in the R740, you should ensure your BIOS and iDRAC firmware are updated to the latest versions before performing the swap.

Excellent reply - that's exactly the information I was looking for! Thank you so much.

@DELL-Josh Cr​ Thanks for the excellent reply. How do risers factor into fan behaviour?

@Anonymous Coward​ 

This might help  - but I ordered a Riser 1A from China and swapped that into the server. No difference in fan speed.

I have to run with a fan offset on medium as the dual rtx6000pros get toasty.

Hi @Anonymous Coward

The thermal factors that can influence fan speeds and acoustic performance on the PowerEdge R740/R740XD are documented on page 28 of the Dell acoustical performance guide:

https://dl.dell.com/manuals/common/dell_emc_poweredge_14g_acoustical_performance_and_dependencies_22nov2018.pdf

The key factors that can affect system acoustics include:

• Ambient Temperature: Higher ambient temperatures may require increased fan speeds to maintain optimal cooling.
• NVDIMMs: Certain workloads and configurations utilizing NVDIMMs may cause fan speeds to increase.
• NVMe SSDs: These drives typically consume more power than SATA or SAS drives and may require additional cooling, leading to higher fan speeds.
• Middle and Rear Drives (R740XD): Installing dedicated middle and rear drives can increase cooling requirements and, consequently, acoustic output.
• GPU Cards: Systems configured with GPGPU cards may operate with significantly higher fan speeds and noise levels compared to standard configurations.
• BIOS Thermal Profile: The default setting, Power Optimized (DAPC), generally provides lower fan speeds and reduced acoustics. Selecting Performance Optimized may increase both fan speeds and system noise.

Based on the information provided in the document riser cards themselves are not identified as a factor that directly impacts the acoustic design or fan behavior of the system. However, if a riser hosts a component such as a GPU or another add-in card that generates additional heat, the system may increase fan speeds to meet cooling requirements, which can result in higher acoustic levels.

In general, when referring to a riser, we are speaking only about the expansion riser card. If no device is installed on the riser, it should not affect fan speeds or system acoustics. If a heat-generating device is installed, changes in fan speed and associated noise levels can be expected depending on the thermal requirements of the installed hardware.

I hope this clarifies your query. 

If keeping your R740 quiet is a priority, I'd lean toward the Xeon Gold 6230. It has a 125W TDP, 20 cores and 40 threads, compared with the 6240's 150W TDP, 18 cores and 36 threads.

The 6240 will produce more heat under sustained workloads, but that doesn't necessarily mean significantly higher fan speeds when the server is mostly idle. Dell's fan control responds to thermal conditions and installed hardware, and Sound Cap should help keep noise down.

One important detail: Dell's R740 thermal specifications call for two 2U standard heatsinks when running dual CPUs above 125W, while six standard fans are supported in the dual-CPU configuration. So if you choose the 6240, make sure you have the correct heatsinks.

Riser 1A itself shouldn't be a major factor in fan speed, although the PCIe card installed in it can influence cooling.

Personally, I'd choose the 6230 if quiet operation is more important than maximum performance. Before upgrading, I'd also verify the heatsink part numbers and current fan configuration against Dell's documentation.

@Mark Franklin​ I can confirm dual 6230 is not a loud setup. I am using the high-performance heatsinks even though they're not necessary, along with standard fans, to give more headroom.