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Proper Power Supply Sizing Guidance

Mega Man

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just bumped into this thread,

wanted to add some great psus,

EVGAs lineup ( g2s/p2s/t2s ) are based off of the superflower leadex, which is an awesome supply ( check out some indepth reviews ) and of course outside of the us the leadex, both are also usually well priced ! theseasonic is great both the g/x/variants i personally swear by seasonics ! - be careful as some of the 1250w seasonics are really 4rail systems !

the other evga linups are really well priced ( NOTTHE NEX [ gen1 ] ) and have great specs as well, ( another quality product ) please make sure you buy quality PSUs the maker doesnt matter, the OEM doesnt matter. a quality psu matters !

some of my rigs run 3.2kws of psus in one rig ! so i have learned far more then i thought i needed to know -also on low loads on psus are now not usually an issue ( almost 100% of current QUALITY consumer psus- dont have many issues on low loads )
 

jgreco

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please make sure you buy quality PSUs the maker doesnt matter, the OEM doesnt matter. a quality psu matters !

Actually, the problem here is that the average FreeNAS user has no way to identify "a quality PSU," especially when buying one online, sight unseen, for a new build.

The maker/OEM does matter in this business. It isn't an absolute. Look at automobile reliability. I notice that Toyota isn't on this list of 10-worst-cars. The Prius C is at the top of the list, though. I can draw some inferences that Toyota tends to produce a better quality car, while Ford tends to produce a crappier car. Not absolutes, but does contribute. I'd say at least half the supplies I've seen fail over the past ten years trace back to Fortron. Fortron is the manufacturer who actually makes supplies sold under the Antec, Thermaltake, Sparkle Power, etc., labels.

The problem is that ANY manufacturer CAN make a great supply, and those manufacturers can also make crappy supplies. The reality of the PC parts marketplace is that end users usually aren't willing to pay the price premium for extreme endurance supplies built with milspec components, so the question becomes "which corners did they cut" and "are those corners safe to cut."

There's lots of discussions of the various details on PSU's, but to actually know, rather than guess, you need to rip the damn things apart. http://forums.anandtech.com/showthread.php?t=2297245 for example is an entertaining thread.

So we don't really care what MIGHT work. Anything MIGHT work. When looking at the options for something solid to suggest to users, I wanted something that came as close to "uncompromising quality" as I could find. As far as I can tell, the Seasonics suggested are that.
 

solarisguy

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So..., after reading all the advice, can some provide feedback how their sizing turned out in real life?

For me: 430W Bronze provides 115W (Xeon E3-1220 v3, 32GB RAM, 8x 3.5" disk, 2x 2.5" disk)
 

jgreco

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That's not really all that useful. I could have *guessed* at that.

8 drives at 6 watts -> 48 watts
2 drives at 3 watts -> 6 watts
E3-12xx CPU and mainboard -> 40 watts
Fans -> 15 watts

109 watts, back of the napkin math.

The purpose of the sizing advice isn't to justify your idle power consumption. It is to make sure that your PSU is large enough that bad things are less likely to happen.

I'll note that your PSU seems to be right on the bleeding edge of "too smallish".
 

Ericloewe

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So..., after reading all the advice, can some provide feedback how their sizing turned out in real life?

For me: 430W Bronze provides 115W (Xeon E3-1220 v3, 32GB RAM, 8x 3.5" disk, 2x 2.5" disk)
Well, @Bidule0hm measured spinup current for a few drives he had lying around, in that other thread.
 

Bidule0hm

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Well, @Bidule0hm measured spinup current for a few drives he had lying around, in that other thread.

The link to it is somewhere in the first post of this thread, and in my signature right below this post ;)
 

Ericloewe

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The link to it is somewhere in the first post of this thread, and in my signature right below this post ;)
That reminds me that I should probably get an oscilloscope. For science.
 

Ericloewe

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Want me to send you a Tek 475? It gets used so little I'm not even sure it works anymore ;-)
The offer is much appreciated, but shipping costs would probably make a brand-new Keysight look like a good deal. :p
 

Bidule0hm

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Yeah, but it's very good old tech :D DSOs... pfff... :P
 

Ericloewe

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Yeah, but it's very good old tech :D DSOs... pfff... :p
The appreciation one has for DSOs is proportional to the amount of captures one is expected to obtain from a 70s vintage 20MHz oscilloscope with no sort of memory.

I can't imagine even trying that stunt with a film camera.
 

Bidule0hm

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Yep, there's some very useful features like captures, pre-trigger data, infinite persistence, advanced math functions, ... but the thing about a 70s scope is that it's a 70s scope that still works perfectly in 2015, I don't think a lot of 2015 DSOs will still work fine in 2060 :)
 

solarisguy

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That's not really all that useful. I could have *guessed* at that.

8 drives at 6 watts -> 48 watts
2 drives at 3 watts -> 6 watts
E3-12xx CPU and mainboard -> 40 watts
Fans -> 15 watts

109 watts, back of the napkin math.

The purpose of the sizing advice isn't to justify your idle power consumption. It is to make sure that your PSU is large enough that bad things are less likely to happen.

I'll note that your PSU seems to be right on the bleeding edge of "too smallish".
I really comment on your posts, since you are right. Here too :D

However, TPD of my CPU is 80W, so in total 200W when busy.

My 3.5" disks are starting 2 seconds apart. Why would my system use more than 300W when starting?

If I misinterpreted spinup current measurements, and the disks should be starting 3 or 4 seconds apart, I will make such an adjustment.

P.S.
When my local supplier starts stocking quality 450W Gold and quiet power supplies, I am buying one.
 

Bidule0hm

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We are at 2 sec/div so you can see pretty much all the drives have a spin-up time of about 6 sec so whatever your staggered spin-up delay is you should use a 6 sec spin-up time in your calculations ;)

Here for example you'll have at most 3 drives spinning up at the same time (6 sec / 2 sec).
 

jgreco

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However, TPD of my CPU is 80W, so in total 200W when busy.

Yes, but the above was an idle power calculation.

My 3.5" disks are starting 2 seconds apart. Why would my system use more than 300W when starting?

Usually there's some work that needs to go into arranging staggered spinup. Either a drive is configured for Power-Up In Standby (PUIS), configuration of which requires you to log into the drive and twiddle a stored parameter (for drives that support PUIS), or an integrated system and backplane which signals spin-up on SATA power pin 11, which I doubt you have, since it is relatively rare except for specialty hardware.

So I'm guessing you've set up PUIS. And that's fine. But the problem I have with that is that over time you forget you set PUIS, or you may end up needing to replace a failed HDD, or you may want to upgrade the pool, and in five years when PUIS isn't supported by Eastern Skydoor (the merger of Western Digital and Seagate), you've then created a situation where what-works-today doesn't work then. Also, it is perfectly possible to tell all your hard drives to spin down, and then simultaneously issue a spin-up command, which will gleefully disregard your carefully designed PUIS strategy.

I like to future-proof and mistake-proof to the extent possible.

If I misinterpreted spinup current measurements, and the disks should be starting 3 or 4 seconds apart, I will make such an adjustment.

P.S.
When my local supplier starts stocking quality 450W Gold and quiet power supplies, I am buying one.

There, too, go look at @Bidule0hm 's awesome spinup current thread, where he does the work I'm too busy^Wlazy to do. The amount of time you need to allow for any given drive to spin up and stabilize varies wildly between drive types.

In the end, I just don't see a lot of value in undersizing a power supply. I certainly know that it CAN be done; in some situations, you virtually HAVE to (think: large numbers of drives). However, for a smallish NAS such as this thread discusses, there are also significant risks.
 

Ericloewe

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jgreco

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*shudders*

Aw, come on, that was funny.

don't forget little gain

I thought that was implicit in this whole thread. Undersizing power supplies doesn't carry much benefit until you're out past maybe 10-12 drives, at which point it starts to make sense to do some engineering of the system.
 

jgreco

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The appreciation one has for DSOs is proportional to the amount of captures one is expected to obtain from a 70s vintage 20MHz oscilloscope with no sort of memory.

No sort of memory? Whatchatalkinabout? I have lots of memories of analog scopes being a PITA to use. :smile: Maybe what I should actually do is go find a nice DSO, huh. Problem is, measuring current in this thread is probably one of the few times in the last few years I even thought about a scope. Can't justify a "nice" five-figure DSO. Are the USB "hook it up to a computer" ones any good? We've got bench PC's and that wouldn't be any trouble.

http://www.ebay.com/itm/Hantek-DSO-...MHz-2CH-250MSa-s-10mV-5V-9Steps-/290749359288
 

danb35

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