VRTX Blower PWM

Question

Hi,

I have a question regarding the PWM of the blowers in the VRTX.

I have latest version of the CMC.

When the chassis is turned on, but no blades turned on the blowers insist on running @ 20%.

First I thought it was because I had AIC's installed, but it persist even if I remove the AIC's.

As I can see from the design of the VRTX, the blower fans seems to be designed to cool the blades only and the fans the remaining parts.

So why is it when the blades are turned off that the blower fans are still running @ 20%.

I have set no offset for the fans and enhanced cooling mode has not been enabled.

I would think the blower fans would either turn off or go even lower down in PWM.

I know its possible to control the fans of dell servers in general via ipmi, but it seems like the CMC does not have an ipmi interface.

Is there any way to make the blower fans run slower?

Supposedly the VRTX should be able to be run under the desk, but I guess you have to be deaf to be able to handle the noise.

DELL-Chris H · Accepted Answer

It is as designed, it is due to the enclosure anticipating the start of the blades, as normally the enclosure won't be ran with no blades installed. So when you power on the enclosure it starts the blowers waiting for you to start the blades. This is why you don't see the same thing when powering down the enclosure, as it isn't expecting the blades to be powered on when it is shut down.

May I ask why you're wanting to run the enclosure with no blades running?

DiegoLopez · Answer

Hello @Bjorn Smith,

The VRTX supports up to four blowers for server nodes, six 60-mm fans for storage and I/O cooling. These six hot-swappable cooling fans that provide cooling to the storage and I/O components in the enclosure.

The CMC Monitors and automatically controls cooling fans based on actual ambient and internal temperature measurements. Some 3rd party add-in cards will need the increase system fan speed response to provide additional cooling.

This is working as designed. Because, even when the blades are turned off, the CMC is still running to provide remote access. We do not recommend modifying this setting because it allows the system to run the CMC safely and provide remote operations.

This being said, you can edit some fans configuration with racadm commands. But the only out of the box configurations for fans are to increase fan speed like the fan offset configuration (racadm fanoffset [-s ]) https://dell.to/2SIU1C5

I know some users were able to edit more advanced fan configurations, so maybe the best option is to let the post open to see if any of them can help you with this configuration.

Regards.

Bjorn Smith · Answer

Hi,

First - thank you for the response, but it seems like you did not read my post properly.

The fans are not the issue - the blowers are.

I am aware that the fans and blowers are controlled based on the sensors and ambient temperature.

Ambient is around 22 degrees celcius and when the blades are off, then fans are running around 6%, which means they don't many noticeable noise.

Please notice this is regardless of any AIC cards are installed at all. When the blades are off, the fans spin down to 6%.

The blowers spin down to 20%, even though they are not needed for any cooling.

And as you have stated, the blowers are for the 4 server blades.

So why are the blowers running @ 20% when all the blades are powered off?

Regards

DiegoLopez · Answer

Ok...

I understand now. So, for example, if you disconnect the VRTX from the power cable and the fans stops totally and you plug in them again, what happens? Do they start running at 20%? Or this only happens when you turn down the system?

Bjorn Smith · Answer

I have now tried to pull the power entirely and power up the chassis only - but blowers still insist on running @20% even if no blades are turned on.

In my opinion that seems to be a bug in the CMC, since the blower are only to cool the blades as far as I understand.

I have attached a couple of pictures to show status/configuration of the VRTX.

Fans/blower powered offTemperaturesPower settingsFans/blowers just after power onCMC infoFans/blowers are full power on of CMC

Bjorn Smith · Answer

Hi,

I haven't tried pulling the power cables.

But when I shut down the chassis and all blades - only one fan keeps running - that is the fan that cools the CMC.

When I power up the chassis, then the blowers start spinning to 20% immediately after power up has completed.

Even if I don't have any blades powered on.

I will try to pull the power from the chassis and power the chassis on again, to see how the blowers react.

Bjorn Smith · Answer

Added a detailed view of one of the blowers. Please notice this is with _ONLY_ the chassis powered up - no blades are running.   Detailled view of blower

DELL-Chris H · Answer

Bjorn Smith,

What you are seeing is by design and it isn't supported to adjust them. You likely can adjust it via IPMI but we don't support it. Now depending on the iDrac firmware version it could causes an increase, what is the iDrac versions you have?

Bjorn Smith · Answer

Hi,

So you are saying that the machine that is adertised to be a machine you have standing under your desk is designed to have blower fans spinning @20% even if its not necessary, since no blades are running?

That seems like a poor design for something to have standing under your desk - I mean what is the point of having blowers running if no blades are powered on? Blowers are for cooling the blades right?

I am not saying its a bug, but if I were the product designer of the VRTX I would demand that blowers would be @ 0% PWM when all the blades are turned off - its not rocket science to have fans turn off when they are not needed.

And as far as I know, the CMC does not have an IPMI interface - it certainly does not respond to any IPMI connections.

My chassis is running version 3.21 - which should be the latest version as far as I know

All the blades are running iDRAC version 2.65.65.65 (M620's). / 2.70.70.70 (M630's)

But I don't see how any of the blades are of relevance since they are powered off.

Basically I am running latest of everything in terms of bios/idrac/firmware as of this date.

Dell-DylanJ · Answer

Hello,

The documentation does indicate that the blowers are for cooling the blade nodes. If I were to hazard a guess as to why they were behaving in that manner, I would guess that it's because they're looking for a signal from the iDRAC that they aren't getting, since the blades would be off. However, that's just a guess, and may be wrong. The actual cooling parameters aren't something that is shared with us, so I don't want to send the wrong impression.

You're correct about the CMC version being the latest. M620 and M630 are on the latest, as well. I didn't see the VRTX infrastructure version mentioned. It's not updated as often, and may be current, but it's definitely worth checking.

https://dell.to/2TlRePA

If this doesn't help, I can't think of anything else.

Bjorn Smith · Answer

VRTX infrastructure is also on newest firmware.

Any chance you can pass this onto an engineer to see if they experience the same - just so I can be sure that it is not my VRTX that is somehow broken or have faulty sensors.

Or does that require a support contract?

Thanks

Bjorn Smith · Answer

Hi,

Naturally I don't plan to run the chassis without blades in it - that would be strange I think - I was just surprised that when no blades was powered on that the blowers were spinning.

And by that design logic, then the normal fans should also be spinning higher as soon as I power on the chassis, but they stay low - probably because they use.

Normal server's dont spin their fans until its needed, i.e. when you power it on - I just thought the same would be true for a blade chassis - I mean it's not like it takes minutes to spin the fans up.

But anyway - if its by design that the blowers run at 20% from the start, then thats it - I just haven't experienced something like that before.

Thank you for all your time.

Regards

Vincent20170210 · Answer

Hi,Bjorn Smith I'm looking for same solution. I would like to ask about how to set fan speed pwm to 5%? Thanks a lot!!

DELL-Chris H · Answer

Vincent20170210,   As previously stated the system is working as designed, and while you may be able to adjust it via IPMI, it isn't supported on our end.

Rack Servers

VRTX Blower PWM

Was this post helpful?