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Proper Power Supply Sizing Guidance

jgreco

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Of course that's not the only number that can be debated. I fricking linked to an actual counterexample. Kindly stop posting misinformation in my thread.
 
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Great guide jgreco. I'm happy to get confirmation that my choice of PSU was a good one for my setup.


Whilst I was reading through the original post, one thing stood out to me. The recommended PSU for a 9 or 10 drive system is the SeaSonic G-550. I'm not questioning the choice of model, I've used Seasonic stuff (including G series PSUs) for as long as I've been building computers but G-550 has only 6x SATA connectors. Which raises the question of what do you folks use for your additional SATA connections (other than Molex power drive cages or backplanes)?

The reason I ask is because I've never had to answer the question myself. I've always had PSUs with enough SATA connections as standard or they've been modular and had room for additional SATA cables.
 

jgreco

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Power distribution is a good question. As with so many things NAS-sy, you have some options, ranging from purchasing additional PSU leads, to making custom ones (or having them made for you), crimping additional connectors onto existing leads, ripping apart some inexpensive drive power-Y's to solder into existing leads, etc.

Around here, we have a well-stocked electronics shop that can engage in a variety of activities. We can make a lot of standard types of cables in-house. For SATA power, I like to cheat and rip apart good quality drive power-Y's, because the molded ends usually don't lose their grip on the cable. :) Cut it up and you get two nice molded ends. Very useful for building a new cable assembly.

A recent discussion, plus a dire warning against just using the SATA drive power "Y"'s as they are sold, is here:

https://forums.freenas.org/index.php?threads/first-freenas-build-verification.38807/#post-237362
 

Ericloewe

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Sidenote: It's possible that currently shipping G-550s have 10 SATA connectors. I haven't bought any recently, so I can't confirm.
 
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I don't know if this is too lame or not but I've found these ;)

Asus Power Supply Guide and PowerSupplyCalculator.net

Between the two I've got roughly 20% difference (which is huge!) the ASUS calculating 400W usage vs 345W on the other for a dual CPU system with E5-2670 and 7 HDDs and 4 DiMM slot used. It looks a bit on the low side but it's OK for a rough estimate...

PSU.PNG

Edit: made some strike through on the (ir)relevant part ;)
 
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jgreco

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I don't know if this is too lame or not but I've found these ;)

Asus Power Supply Guide and PowerSupplyCalculator.net

Between the two I've got roughly 20% difference (which is huge!) the ASUS calculating 400W usage vs 345W on the other for a dual CPU system with E5-2670 and 7 HDDs and 4 DiMM slot used. It looks a bit on the low side but it's OK for a rough estimate...
Oh yeah? Off by more than 100% is OK for a rough estimate? Here's a clue: don't use them unless they explain their math.

345 watts? Frak, the CPU, mainboard, and RAM by itself is capable of burning 300+. 115 watt TDP CPU's times two, 24 watts memory, 60 watts mainboard, system fans, etc., I can get that system without any disks at all cooking at over 300W no prob.

I'm very careful in the first post here to show how and why I've arrived at the numbers I do, and they've been done for a system that is expected to be heavy on the disks. There's also a fair bit of safety margin built into the numbers here.

I'd put the power requirement at closer to an 850W PSU. Please go back to the first post in this thread. Read the first sentence of this first post. Imagine that I am saying that directly to you. Because I am.
 
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Please go back to the first post in this thread. Read the first sentence of this first post. Imagine that I am saying that directly to you. Because I am.
I know, I know - I've read it yesterday :oops:
And I would not dream of running the thing from a £10 PSU anyways. I don't want to be a statistic ;)
 

jgreco

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I know, I know - I've read it yesterday :oops:
And I would not dream of running the thing from a £10 PSU anyways. I don't want to be a statistic ;)
Well, fine, then. All I want is for people to make informed, educated choices... because it's so damn depressing to have people come on in and say "but I didn't know that was bad, plus, is there any way to recover all the baby pix of my kids".
 
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Well, fine, then. All I want is for people to make informed, educated choices...
As we discussed this in a parallel galaxy (thread) I just felt my nice and shiny 920W redundant platinum rated PSU is a bit over the top. According to the manual I can also set up the mobo so the HDDs won't try to spin up at the same time so I can reduce the stress on the PSU.

PS. I also made some edit on the aforementioned post ;)
 

jgreco

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As we discussed this in a parallel galaxy (thread) I just felt my nice and shiny 920W redundant platinum rated PSU is a bit over the top. According to the manual I can also set up the mobo so the HDDs won't try to spin up at the same time so I can reduce the stress on the PSU.

PS. I also made some edit on the aforementioned post ;)
Yeah, sorry if so, hard to keep track. The 920 isn't really that much over the top if the numbers can be calculated at 850. Sure, you can do design tricks such as avoiding parallel spinup, but it's just another thing to keep track of - and to forget when one day you "reset BIOS to defaults" in ~3-4 years and you totally don't remember that this is an issue.

Again, informed, educated choices.
 

Stux

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"~15-30 watts per fan"

Is this right? I've been looking at fan datasheets and they range from 0.96W to 4.56W for the fans I've checked between 80mm and 120mm.

Summing the 8 fans in my planned system I come to 25W total. Using the guidance, 8 fans at 30W each, that'd be 240W, which is more than the drives are supposed to use!
 

Ericloewe

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Stux

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Depends on the fan. What fans are you looking at?
Currently using the default case fans, and a pair of Noctuas CPU fans

3x 120mm case fans :
FUHE MOTORS DC1202512H
found this spec sheet: http://www.impedanca.si/media/KLD024PP120CSWH.pdf
4.56W max

2x 80mm case fans:
Delta 80mm AFB0812H
0.24A on the fan label = 2.88W

and two Noctua 90mm NF B9 PWM, fan and specsheet says 0.96W

And I think I will add a fan over the PCIe cards for HBA/NIC/SSD cooling, etc
 

Ericloewe

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FUHE MOTORS DC1202512H
found this spec sheet: http://www.impedanca.si/media/KLD024PP120CSWH.pdf
4.56W max
Seems reasonable.

Delta 80mm AFB0812H
0.24A on the fan label = 2.88W

and two Noctua 90mm NF B9 PWM, fan and specsheet says 0.96W
Delta and Noctua are generally trutworthy, so their specs should be fine, too.

In any case, it's good practice to add a bit of a margin to allow for spikes on spinup, in case the datasheet has been embellished.
 

anodos

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Currently using the default case fans, and a pair of Noctuas CPU fans

3x 120mm case fans :
FUHE MOTORS DC1202512H
found this spec sheet: http://www.impedanca.si/media/KLD024PP120CSWH.pdf
4.56W max

2x 80mm case fans:
Delta 80mm AFB0812H
0.24A on the fan label = 2.88W

and two Noctua 90mm NF B9 PWM, fan and specsheet says 0.96W

And I think I will add a fan over the PCIe cards for HBA/NIC/SSD cooling, etc
Desktop cooling fans and server cooling fans are a bit different. Server fans need to be able to force a lot of air through a densely-packed chassis, and they tend to consume a lot more power. See this datasheet for reference:
http://www.supermicro.com/support/resources/Thermal/
 

Stux

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Desktop cooling fans and server cooling fans are a bit different. Server fans need to be able to force a lot of air through a densely-packed chassis, and they tend to consume a lot more power. See this datasheet for reference:
http://www.supermicro.com/support/resources/Thermal/
Thanks :)

Still, an estimate of 15-30W per fan, when some 'rigs' may have 10-20 low wattage fans, could result in some serious over-sizing of PSUs

Its unfortunately, more like 1-36W :)
 

jgreco

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Summing the 8 fans in my planned system I come to 25W total. Using the guidance, 8 fans at 30W each, that'd be 240W, which is more than the drives are supposed to use!
You do have to account for some extra to start the fan, plus it's a good idea to measure stall current consumption and assume one of your fans will do that. You're using more fans than most people would, so it isn't going to hurt you if you use real numbers for your gear and then add a little margin.

Thanks :)

Still, an estimate of 15-30W per fan, when some 'rigs' may have 10-20 low wattage fans, could result in some serious over-sizing of PSUs

Its unfortunately, more like 1-36W :)
Between 1 and 36W?

The San Ace 40 counter-rotating 9CR0412S513 is a 40mm fan that eats 13 watts.

The Delta TFB1212GHE-F00 is a 120mm fan that eats 30 watts.

The Sanyo Denki 9CR1212P0G03 is a 120mm fan rated at 87 watts.

A PSU that is too large is generally much less dangerous than an undersized PSU.

For the typical server build, you're going to have three or four chassis fans. If you're trying to build a quiet low power NAS, things change. That's why I do say

and ~15-30 watts per fan.
but that statement is *immediately* followed up by:

Honestly it can be a fair amount of work to come up with a good number, take some time and look at data sheets.
I mention the fans because people often discount X, Y, and Z when doing their server builds, and come to the conclusion that their 300W PSU can safely power 12 drives because "8 watts!!!!!!!!!!!!! times 12 is only 96!!!!!!!!!!" I know it's totally crappy but the sad fact is that hard drives suck. Current, that is. Suck current. And so do all these other little doodads like fans. In the end if you take what I've outlined and apply it to your particulars, being mindful of the mistakes I'm trying to highlight, you ought to wind up with a safe PSU size.
 

Ericloewe

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VladTepes

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