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Proper Power Supply Sizing Guidance

Glorious1

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Excellent guide. I just found it, but wish I had something like it when I built my system. I ended up with a Seasonic Platinum Fanless 400.

When I calculate through your guide, assuming the 10 drives my case holds, I should have a 522-watt PSU. However, I have only 7 drives in it, for which the calculations suggest a 390-watt PSU. Guess I won't be adding more drives! (I don't have enough SATA power connectors for them anyway). Luckily my Noctua fans have maximum input power < 1 watt each.
 
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Thankfully I'm just finding this thread before something has happened and I might be okay but I just wanted to check. I am having a hard time tracking down potential watts, potential 12v amps and average idle watts for all my components in the tech documents that I can find. Here are my best estimates and my components if someone has the heart to give me a rundown:

(Potential Watts, Potential 12v amps, Average Idle)

2.5" HDD:
Hitachi HTS542580K9SA00 (5w,?,.8w)
Hitachi HTS542580K9SA00 (5w,?,.8w)
WDC WD1600BEVT-75A23T0 (?,?,.85w)
SAMSUNG HM160HI (4.5w,?,.6)

3.5" HDD: Peak power is listed at 950 ma at 5v is 4.75 (but how could that be less than average idle)
ST3000DM001-1ER166 (4.75w,?,5.4w)
ST3000DM001-1ER166
ST3000DM001-1ER166
ST3000DM001-1E6166

motherboard:
m5a78l-m usb3 (no idea OP says ~25w)

CPU:
AMD Athlon IIX3 (95TDP)

RAM:
4x4gb hmt451u7afr8c (no idea OP says ~6perstick total of ~24)

LanCard:
intel pro/1000 gt desktop adapter (8w)

HBA:
Dell h200 card (no idea OP says ~10w)

Fans:
2x80mm front (.96w,.08,?) total of 2w
92mm rear (no idea)
120mm front (no idea)
cpu fan (.20a 12v)=.24w

Based on my initial work I have:
8x5w~~40watts HDD
25w motherboard
95w cpu
24w ram
20w Cards
~10w of fans

Total is 214W.

I have it running on a Corsair cx430. I know not recommended which is why I'm here.

http://powersupplycalculator.net/ gives me estimates of 82W idle 192 load and a 274 recommended power supply

Which is pretty close an except for perhaps having a crap PSU I am seemingly in the right range for what I need.

The biggest question are my Seagate Hard Drives and here is the pdf where I got the info:
http://www.seagate.com/www-content/datasheets/pdfs/desktop-hdd-8tbDS1770-9-1603US-en_US.pdf
 

Ericloewe

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Thankfully I'm just finding this thread before something has happened and I might be okay but I just wanted to check. I am having a hard time tracking down potential watts, potential 12v amps and average idle watts for all my components in the tech documents that I can find. Here are my best estimates and my components if someone has the heart to give me a rundown:

(Potential Watts, Potential 12v amps, Average Idle)

2.5" HDD:
Hitachi HTS542580K9SA00 (5w,?,.8w)
Hitachi HTS542580K9SA00 (5w,?,.8w)
WDC WD1600BEVT-75A23T0 (?,?,.85w)
SAMSUNG HM160HI (4.5w,?,.6)

3.5" HDD: Peak power is listed at 950 ma at 5v is 4.75 (but how could that be less than average idle)
ST3000DM001-1ER166 (4.75w,?,5.4w)
ST3000DM001-1ER166
ST3000DM001-1ER166
ST3000DM001-1E6166

motherboard:
m5a78l-m usb3 (no idea OP says ~25w)

CPU:
AMD Athlon IIX3 (95TDP)

RAM:
4x4gb hmt451u7afr8c (no idea OP says ~6perstick total of ~24)

LanCard:
intel pro/1000 gt desktop adapter (8w)

HBA:
Dell h200 card (no idea OP says ~10w)

Fans:
2x80mm front (.96w,.08,?) total of 2w
92mm rear (no idea)
120mm front (no idea)
cpu fan (.20a 12v)=.24w

Based on my initial work I have:
8x5w~~40watts HDD
25w motherboard
95w cpu
24w ram
20w Cards
~10w of fans

Total is 214W.

I have it running on a Corsair cx430. I know not recommended which is why I'm here.

http://powersupplycalculator.net/ gives me estimates of 82W idle 192 load and a 274 recommended power supply

Which is pretty close an except for perhaps having a crap PSU I am seemingly in the right range for what I need.

The biggest question are my Seagate Hard Drives and here is the pdf where I got the info:
http://www.seagate.com/www-content/datasheets/pdfs/desktop-hdd-8tbDS1770-9-1603US-en_US.pdf
Did you miss this part of the OP?

Calculating How Much Power You Need

The big thing that most people miss when figuring power consumption is drive spinup current. Most drives take up to about 2.1 amps of additional current on the 12 volt rail to start the platters spinning - that's 25 watts per drive. This is in addition to the eight watts that the drive electronics may be consuming. Do note that some drives use less power, and some use more.

I do not particularly like to undercalculate power requirements, because that may lead to voltage sag, which then leads to equipment failure. Some current drives require a lower amount of spinup current (~1.7A) but I encourage you to contemplate that drives might be replaced or upgraded. Running things right on the edge is a bad idea. If you are building a system with more than four drives, I encourage you to look at the specifications for your drives, but still suggest that you want to reserve about 35 watts for each drive.
That calculator, like most found on the internet, is close to worthless, as proven by real data. So you need to add a bare minimum of 100W to your estimate.

The CX430 is pretty crappy. It's an old group-regulated design, which means uneven loads are going to be painful.

In practice, the minimum-quality power supply we recommend is the Seasonic G-450, which would work in your case - G550 if you want to expand. There's just no good justification for using crap PSUs these days.
 
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Did you miss this part of the OP?


That calculator, like most found on the internet, is close to worthless, as proven by real data. So you need to add a bare minimum of 100W to your estimate.

The CX430 is pretty crappy. It's an old group-regulated design, which means uneven loads are going to be painful.

In practice, the minimum-quality power supply we recommend is the Seasonic G-450, which would work in your case - G550 if you want to expand. There's just no good justification for using crap PSUs these days.
Thanks for running it down!

I did read the part of the OP about spin up and that is what I understand "Potential Watts" to mean. So I guess my question about hard drives remain.

Starting with the Seagate:

That PDF says the following: "Startup Power (12V, A): 2.5" for my model. I understand that to me spin up so that would be 30W (now i see i messed this math up in my first post and here is the extra 100W!)

so 4x30 for the seagats =120

For the 2.5"
Hitachi this is what the tech doc says: "Startup (maximum peak) 5.0 W"
WD this is what is says: "5VDC ±10% (A, peak) 0.950" which i equal to 4.75W
Samsung says: "Voltage +5V±5% Spin-up Current (Max.) 900 mA" which i equal to 4.5W

Is that right for 2.5" drives... around 5W

so 2*5+4.5+4.75=19.25

So correcting my original math: 140W HDD
25w motherboard
95w cpu
24w ram
20w Cards
~10w of fans

Total ~320

*1.25 from original post = 400
*.20 from original post = 64

I got around 110 for my idle assuming an 80% power drop off to idle for everything except my ram, motherboard and fans.

400 is my target

And this from OP:
Multiply that number by 0.20. If the result is less than your average idle watts, you have a power supply size that's going to be in the efficiency sweet spot for a high quality PSU.

Yes 64 < 110

So it looks like the Seasonic G-450 is the one for me and like you said the 550 if I want to expand.

I'll punt the crap Corsair.

Thanks!
 
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Supermicro X11SLL-F-O: ~25W
1 x 16 UDIMM RAM: ~6W
Celeron: 51W
6 x 3TB WD Blues: ~23W peak (source)
Fans: ~30W (I think this is generous for the fans I'll use are each around 3-4W)

Total peak: ~250W
Target size: 312W
Total idle: ~60-80W (rough guess)

Thinking of a SS 450 for some buffer room, and going by the TL;DR.
 

Ericloewe

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6 x 3TB WD Blues: ~23W peak (source)
That's rather optimistic, given the real measurements we've seen. Additionally, the measurements are for 5400RPM drives, so 7200RPM drives are likely to need more power to spin up.
 

Ericloewe

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Stux

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Blue is the the new green ;)
 

brando56894

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I stumbled upon this thread again after seeing it mentioned in one of the Will It FreeNAS? threads and decided to give it another read since I have upgraded my hardware in the last 6 months or so. I have 11 HDDs (7 are 7200 RPM, 4 are 5400 RPM), 2 SSDs and an NVME drive, along with an 8 port HBA, 5x 120mm fans and a SuperMicro X10SDV-F which has an integrated Xeon D1540. My calculated total wattage was around 730 watts....I seemed to remember that the PSU in my case was a lot smaller than that but I couldn't get to it because NZXT hides it away under some odd shroud in the H440. I forgot I had my PSU in my signature... it's only 450 watts!! how the hell have I been surviving on that? o_O
Granted 3 of the HDDs and the NVME drive were added in the last month and the X10SDV was added in about 6 months ago when my C2750 bit the dust, at that point I had a SilverStone 600w SFX PSU in it but sold it with my DS380 because I thought it had killed the board (CoD was most likely the watchdog issue that plagues the boards), so when I bought a new case and a new board I threw in a 450w SeaSonic PSU I had laying around, since I didn't have the money to be buying a new board and case in the fist place and figuring that would be enough.

I've been running a mix of ESXi 6 with multiple VMs, Arch Linux with KVM and ZoL, and FreeNAS 10, and the last one is the only one I've had stability issues with, which I attribute to the development. The only voltage related errors that I've seen are for VBAT, which I'm going to assume is the CMOS battery.

Just to be on the safe side (even though I don't have the money for it, once again) I just bought a 1 KW SeaSonic PSU that has 16 SATA power connectors. Lack of power connectors is definitely a problem with my current PSU since I believe it only has 8 or 10, so I've been using a bunch of molex to sata adapters but I've run out, so I have one 4 TB drive that will be used as a spare sitting unplugged. Seeing the (theoretical) lack of power, the actual lack of connectors and the fact that FreeNAS 10 will soon become release quality, I want to have the most stable system when I'm running it and my VMs under heavy load.
 
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Already have a SeaSonic G-650 650W PSU to power 11 HGST 7200RPM Deskstar Nas drives...using a Xeon E3 1230 V5 and 8 PWM fans of 120mm-140mm sizes. Do I need to return the 650W in favor of the 750W version? I originally purchased it with the intention to use 10 drives, but later decided to do 11.

Edit: nvm, just to be safe I returned the 650W and ordered the 750W since it was the same price anyways.
 
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Evi Vanoost

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My advice if you're going to create your own boxes:
Look at what the 'big boys' put in their systems. Look at AIC or SuperMicro n-slotted devices (either NAS or DAS) and your power supply should be sized pretty closely to that to be 'safe'. Obviously a low-power 16 slot NAS with staggered spin-up can probably be done with a high quality 500W (160W for the drives + 200W for the CPU) but you can't expect to put a dual high-end Xeon with a TDP of 150W each and a GPU.

It's hard to calculate even as an electronics engineer. You not only have to calculate peak power usage of your drives but also losses caused by the lengths of wire, since it's all low-voltage DC, any length of wire will experience some sort of loss, not a big problem for 4 drives, but for 48 drives across 8U this will count.

Also calculate for the fact that some times, failing drives may stress your system. You should also account for controllers, CPU and motherboard, memory, expanders, fans, power surges or brown-outs and the fact that power supplies are not 100% efficient. And then look at whether you want to eventually upgrade or replace failed drives, replacing a power supply just because your new drives consume a few more watts is just a waste of money.

The other issue, especially with cheaper power supplies is that 750W means 750W peak. You can only pull 750W (if even that) for a fraction of a second or perhaps a few seconds before it goes into protective mode or blows something. That being said, my 12 bay NVMe system uses 'just' 200W under average load and ~360W during startup with dual Xeon's and 16 RAM modules.

Well designed SMPS power supplies, even if you buy one that has a 20-40% higher rating than the other will not use significantly more power under the same load. You can obviously buy quality power supplies that have better ratings, but if you really want to save on power, go with SSD's instead of HDD's.
 
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Ericloewe

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I find @jgreco's numbers very conservative, which is good. For the average inexperienced user, it's a very useful reference.
 
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I also have experience with sata and ide splitters
If you intend not to go bold early
do your best not to get splitters
My experience with them is unpleasant
Under load drives will disconnect
Whille it started with 1 it developed to 3 having problems
Evin a silverstone sata splitter developed the same problem
 

farmerpling2

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If you have to choose between a PSU with 92% or 85% efficiency, choose the first one. It cost more, but the price between them (BEP), is earned back within a year.
A little late to add on to this thread, but it seems like no one reads the specs (especially charts) showing efficiency.

Generally speaking, the best efficiency for most PSU's is at 50% load. The efficiency is lower at 20% (~4% - 6%) and increases at 50% (most efficient) and then drops down as the load increases to 80% (~4% - 6%).

Check out the specs from the manufacturer to get a rough idea on performance of PSU.

IMO, the Platinum or higher efficiency are not worth the extra money. For a server, I would get Gold, because of better parts (longevity), warranty, and a small savings in power.

I personally buy a quality PSU that has 2x the max load for a 1 rail system, that gives me the best efficiency, longevity, warranty (leading to less headache), lower A/C usage, expandability, etc.

A lot of the large server manufacturers push the PSU pretty hard - 80%+ is not unusual in my experience. They are not usually so worried about efficiency, but about having a cheaper server than the competitor that is decent in quality. When using 2 rail redundant PSU's, you want them to use about 40%-45% of load so if one PSU drop's it is running at 80%-90% load on the leftover PSU.

FWIW, My 2 cents.
 

Ericloewe

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A lot of the large server manufacturers push the PSU pretty hard - 80%+ is not unusual in my experience.
They have to. Server power density is huge and there's very little room to spare for PSUs and PDUs.
 

farmerpling2

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Obviously a low-power 16 slot NAS with staggered spin-up can probably be done with a high quality 500W (160W for the drives + 200W for the CPU)...
If you get a motherboard that does not have the staggered spinup, then you should get a different one. For any realistic server MB, they will staggered spinup and typically set it at 3 sec interval. Most drives spinup in less than 3 sec, but there are some it takes almost 4 sec. Good gaming MB even have it... Many enterprise disk farms have hardware staggering built in so MB does not need it - generally high end and expensive.

I disagree with the thinking that you should calculate 30w per drive. That ends up being a gross waste of money for a PSU. With staggering you should use the calculation something like the following:

25watt + (( Num_drives - 1 ) * HD_watt_usage ) = Disk_drive_power_usage

HOME: (5400 RPM or 5900 RPM) HD_watt_usage = 5
BUSINESS: (7200 RPM) HD_watt_usage = 9

The 5 or 9 watt could actually be higher/lower, depending on your drive types (i.e. 10K RPM is higher, 5400 RPM is lower, SSD even lower, etc.) Look at the disk price analysis spreadsheet that I have created. It gives power usage for many NAS drives.

5400 RPM vs. 7200 RPM - There is a difference

I have read where some think that 7200 RPM drives are not worth buying because of dubious performance differences. There is absolute performance increase between 5400 vs. 7200 drives. In rotational speed it is 33%. It is quite common to have better overall performance for all aspects (i.e. seek time, etc.) Of course the power & heat generation will go up, but not by a large amount in the overall picture.

The main reason to choose one speed over the other is your requirements. What is your I/O load?

If your I/O load is 10/sec, 5400 RPM is fine (e.g. general home usage). If your I/O load is 30+/sec then 7200 RPM is better.

Commercial/enterprise businesses will not want to use home/pro-home quality drives. If you are running your business on a 16+ array, then you should look strongly at enterprise quality drives. They cost more, but they also have better quality parts and will fail less than home drives, longer warranty's, etc.

You get what you pay for.

FWIW, mt 2 cents
 

Ericloewe

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If you get a motherboard that does not have the staggered spinup, then you should get a different one. For any realistic server MB, they will staggered spinup and typically set it at 3 sec interval. Most drives spinup in less than 3 sec, but there are some it takes almost 4 sec. Good gaming MB even have it... Many enterprise disk farms have hardware staggering built in so MB does not need it - generally high end and expensive.

I disagree with the thinking that you should calculate 30w per drive. That ends up being a gross waste of money for a PSU. With staggering you should use the calculation something like the following:

25watt + (( Num_drives - 1 ) * HD_watt_usage ) = Disk_drive_power_usage

HOME: (5400 RPM or 5900 RPM) HD_watt_usage = 5
BUSINESS: (7200 RPM) HD_watt_usage = 9

The 5 or 9 watt could actually be higher/lower, depending on your drive types (i.e. 10K RPM is higher, 5400 RPM is lower, SSD even lower, etc.) Look at the disk price analysis spreadsheet that I have created. It gives power usage for many NAS drives.

5400 RPM vs. 7200 RPM - There is a difference

I have read where some think that 7200 RPM drives are not worth buying because of dubious performance differences. There is absolute performance increase between 5400 vs. 7200 drives. In rotational speed it is 33%. It is quite common to have better overall performance for all aspects (i.e. seek time, etc.) Of course the power & heat generation will go up, but not by a large amount in the overall picture.

The main reason to choose one speed over the other is your requirements. What is your I/O load?

If your I/O load is 10/sec, 5400 RPM is fine (e.g. general home usage). If your I/O load is 30+/sec then 7200 RPM is better.

Commercial/enterprise businesses will not want to use home/pro-home quality drives. If you are running your business on a 16+ array, then you should look strongly at enterprise quality drives. They cost more, but they also have better quality parts and will fail less than home drives, longer warranty's, etc.

You get what you pay for.

FWIW, mt 2 cents
We've been through this.

If you get a motherboard that does not have the staggered spinup, then you should get a different one. For any realistic server MB, they will staggered spinup and typically set it at 3 sec interval. Most drives spinup in less than 3 sec, but there are some it takes almost 4 sec. Good gaming MB even have it... Many enterprise disk farms have hardware staggering built in so MB does not need it - generally high end and expensive.
You should never rely on staggered spinup. It's far to easy for it to stop working.

I disagree with the thinking that you should calculate 30w per drive. That ends up being a gross waste of money for a PSU.
We disagree. The 30W number is derived from empirical measurements. You'll also note that Supermicro sizes PSUs similarly to what we suggest.
 

farmerpling2

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You should never rely on staggered spinup. It's far to easy for it to stop working.

We disagree. The 30W number is derived from empirical measurements. You'll also note that Supermicro sizes PSUs similarly to what we suggest.
Yes, it has been discussed, but IMHO, the suggestions are flawed.

Generally, the default for many/most BIOS's that have it, is 3 seconds. If it is the default, it is pretty hard for it to "stop working." I have never seen it "stop working," but I am just one data point around many systems from many vendors.

So one company (Supermicro) sizes as you suggest. Maybe their BIOS is buggy or they have other problems - I do not know. I can tell you from experience and from reading specification sheets, most of the large computer vendors do not size that way (guessing). They do actual measurements and post their data sheets, as such. They use expensive equipment to verify max, etc., so that they do not get sued by some company using their product.

To suggest empirical measurements are better than actual measurements is why some random number is being used (30w). You could say if 30w is good, let's go with 35w just to be safer.

To randomly say, "You should never rely on staggered spinup." just said, "Do not trust BIOS and many of the settings can randomly change on you."

No one says that and we should not say that here, unless there is a BUG in someones BIOS that has not been fixed and people need to be notified.

I disagree with your suppositions and felt that people need to be aware there is more to this than guessing.

Please do not take this personally, but it needed to be said, because the facts say otherwise, in my too many years in the industry. You do a lot of good and help a lot of people.

My best to you.
 
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