6.8.3 SUPERMICRO REPLACEMENT POWER SUPPLY/FANS QUESTIONS

[nerbonne]

First, I have a Supermicro SC846E16-R1200B chassis, which has two redundant 1200 Watt gold power supplies.  PN: PWS-1K21P-1R.  I want to get the super quiet power supplies.  Just want to double check my research, it looks like the 1200 Watt replacement power supply is PN: PWS-1K28P-SQ.  Do I have to use the 1200 Watt version, or can I go with the 900 Watt version, PN: PWS-920P-SQ.  One note, I'm running on 220v power, and my UPS says that the server is pulling just under 400 Watts with the CPU's at as close to 100% load as I could get.  Would I be correct then that at 110v that the max it would pull would be about 800 Watts.  The difference in price is about $30, is it even worth it to skimp the $60 or should I just get the 1200 Watt versions and call it good.

 

Secondly, there are 5 internal 80 mm fans.  The 3 in the middle are 53 dBa and 73 CFM, and the two at the back are 47 dBa and 60 CFM.  I'm looking at replacing them with Noctua NF-R8 redux-1800 PWM fans, which are 17 dBa and 31 CFM from what I can see.  It's a significant reduction in CFM, but I'm not running any 10/15K drives, all are 7200 or lower RPM.  I was also looking at youtube videos where they suggest taping the breather holes on the sides which are there to keep the stock fans from starving.  Any thoughts on using the lower CFM fans?  Do you think it's ok?  I've seen some posts where they put in a 120mm fan wall, I don't want to go that route.  Of note, my house is kept fairly cool, 24 C/75 F.

 

Third, can't seem to find any data on how loud the "Super Quiet" Supermicro power supplies are.  Does anyone know?

[Frank1940]

PS rating for the instantaneous max power which is NOT what you see when looking at power consumption.  With Unraid, the instantaneous max power occurs on the +12V buss in a couple of seconds when all of the disks are being spun up simultaneously for shutdown or parity checks.  (HD peak current requirements on the +12V buss are between 2 and 3 amperes per hard drive!  Finding the exact figure is often difficult as not all HD manufacturers provide it.) 

 

Furthermore, you have to take the max current ratings on each voltage buss with a grain of salt.  As an example, the max current ratings on the +12V buss are such that the power on that buss is virtually equal to the max power rating of the entire supply.  When looking at PS specs, you must consider all of the maximum ratings.  When any Max rating is exceeded for even a millisecond, bad things are going to happen!  These supplies have protection circuits built in and often shut the voltage buss down entirely (i.e., zero volts out!).  Exceeding the PS total max could cause the PS to completely shutdown. 

 

A modern high efficiency PS (which any super quiet PS is going to have to be as it must generate very little internal heat to reduce cooling requirements) is a very complex electronic design with little margin for any overloads. 

 

Cooling fans.  I am not going to go into looking at the various models with you. I seem to recall that folks do replace stock fans on many of the server type enclosures (and yours will hold 24 drives).  (What is the max number you  intend to use???)  The trick is to find better engineered fans that are quieter by design.  Noctura is a company that is doing that so you are in the right ballpark to getting there.  Now, they make many different fans.  Do not go for the absolute quietest fan you can find.  Go for one that will move a substantial amount of air against a reasonable head. (Those tightly packed disk enclosures are a cooling nightmare!)  Noctura makes some models that do this but they are not the quietest ones in their line but they are substantially quieter than what the stock case has.  (I suspect these were selected more for cost than anything else.) 

 

Obviously, taping over the side holes will increase the air flow over the drives.  But that increases the requirement for being able to move air over the drives-- i.e., moving air against a head.  (First law of engineering, you never get something for nothing!)  400W CPU load is a pretty big burden to start with.  You are going to need substantial air flow just to handle that!  You are going to be putting a lot of BTU's into the room/space just from that alone.  That will make it difficult to hold the ambient in the vicinity of the case to 75F.   

[nerbonne]

So it sounds like your saying get the 1200 Watt PSUs and get some fans that are a bit louder and have more CFM?

[JonathanM]

11 minutes ago, nerbonne said:

have more CFM

cfm isn't the important metric, it's static pressure.

[Frank1940]

Basically, Yes.  You could carefully analyze that you could use the 800W supply but that is a big reduction from the 1200W standard unit. 

 

On the fans, absolutely! 

 

One more thing to consider is to consider putting sound absorbing material on the outside of the case-- avoid the intake and exhaust vents.  You could also consider sound isolation feet to prevent transmitting sound energy to the mounting surface.  You could gain another 2-3DB reduction in the sound levels. 

[Frank1940]

3 minutes ago, jonathanm said:

cfm isn't the important metric, it's static pressure.

Very true to a point.  But the two do interact together to get adequate cooling in a particular situation.  I do know that Noctura has (at least when I last investigated) graphs that show CFM verses static pressure (head)  for their entire line of fans on their website.  While these may not seem to be very useful to the average consumer, they do show which fans do better in providing adequate airflow in problem situations. 

[JonathanM]

My point is that you can ignore CFM, and purchase purely by comparing static pressure vs. db and choosing the highest static pressure at a db level you can live with. That chosen fan WILL have plenty of CFM in free flow, but it would be foolish to pick a db number and choose the fan with higher CFM vs the one with higher static pressure at that db number.

 

If the fan can't push air past the restriction, it won't flow the CFM number. Period.

 

This whole argument changes depending on the primary heat load in the computer case. Typical PC's the CPU and RAM is the primary heat load, and if it's a gaming PC, the graphics card is the primary heat load. In those situations, where the CPU and GPU have their own dedicated local cooling, it's the job of the fan wall to keep the ambient air inside the case as cool as possible with as many air changes as possible through mostly wide open vents. CFM rules in that situation.

 

Hard drives don't have dedicated local cooling, and are packed close together, typically with little consideration for mass cooling. We've got to ensure that all incoming cool air is forced around the hard drives. If the case is pulling air in that bypasses the drives, any work we do trying to cool the drives is negated.

[Vr2Io]

On 9/4/2020 at 6:26 PM, nerbonne said:

Would I be correct then that at 110v that the max it would pull would be about 800 Watts.

No, it still pull ~400w, but why you feed 110v instead 220v ??

 

On 9/4/2020 at 6:26 PM, nerbonne said:

can I go with the 900 Watt version, PN: PWS-920P-SQ

Yes in current loading.

 

On 9/4/2020 at 6:26 PM, nerbonne said:

Of note, my house is kept fairly cool, 24

How about current disk average temperature ( all spin up ) ? I expect ~40-43c

Edited September 5, 2020 by Benson

[ChatNoir]

2 hours ago, Benson said:

No, it still pull ~400w, but why you feed 110v instead 220v ??

Probably because a large part of the american continent runs on 110V, not 220V as most of the rest of the world does.  

[Vr2Io]

Next, does OP won't use existing 220v UPS. I doubt market have 110v only PSU, too.

Edited September 5, 2020 by Benson

[nerbonne]

Yes, I am an American currently living in a country that uses 220v.  When I go back to America, I will be running the server on 110v.  The average disk temp is 35.5C (hottest disk is 41C) and the CPU is 39C.  This is with the ear splitting stock fans.  I think I can put in some quieter fans and the temps will go up a bit.