PSU for 24-disk build (single-rail? 5v power?)

[kakburken]

Looking for a PSU for my unraid build but having a hard time figuring out what to buy.

 

I know that I will need at least a 900w if I'm not going to run staggered in unraid (so it can handle spin-up of all drivers simultaneosly) and not lower than 700w if I'm going to be around 50% in load (i assume that is whats optimal).

 

What I don't know, however, is whether it "must" be single-rail, if it's a strong recommendation or if I can just ignore that and buy whatever.

Also i have been trying to find out if the PSUs I've looked at are single-rail or not, but haven't found a single PSU on any of the major webshops (at least here in sweden) that advertise whether it's single-rail or multi-rail, etc on the product pages on the webshops..

 

Also, I read something about buying a PSU that has enough power at 5V (because the HDD uses it during spin-up/boot or whatever.. can't remember exactly why, was something with the HDD anyway). Even this information seems hard to find about the PSU's.

 

I might add that all these "suggestions" ive found here at the unraid forums.

 

So, now im hoping that there is a veteran in unraid who knows about this or someone who knows PSU (or maybe both) and can guide me to a PSU purchase, but above all perhaps answer the questions regarding the single-rail and the 5V thing at least.

[ConnerVT]

One man's opinion:  I believe that folks generally overbuy when selecting a PSU.  But then, some of the funkiest, most difficult problems I've ever troubleshot came down to a marginal PSU.

 

For most people, I recommend buying from a reputable brand, and never buying their budget/discount line.  Many of the PSU from different brands are made in the same factory, only differentiated by the components spec's by the brand/company.

 

But then, I never have been asked about a system with 24 drives.  What you can source in Sweden makes it more difficult to offer advice, other than see what Tier A power supplies in this list fit your requirements: https://cultists.network/140/psu-tier-list/

 

Edited June 25 by ConnerVT
speeling

[kakburken]

27 minutes ago, ConnerVT said:

One man's opinion:  I believe that folks generally overbuy when selecting a PSU.  But then, some of the funkiest, most difficult problems I've ever troubleshot came down to a marginal PSU.

 

For most people, I recommend buying from a reputable brand, and never buying their budget/discount line.  Many of the PSU from different brands are made in the same factory, only differentiated by the components spec's buy the brand.

 

But then, I never have been asked about a system with 24 drives.  What you can source in Sweden makes it more difficult to offer advice, other than see what Tier A power supplies in this list fit your requirements: https://cultists.network/140/psu-tier-list/

 

Thanks for that list! I’ll go thru that list and see if I find something I like.

 

 What’s your opinion about the single-rail va multi-rail? And regarding 5v power?

Edited June 25 by kakburken

[ConnerVT]

With electrical engineering as my college major, but spending the majority of my life in the digital world (but playing a bit with amateur radio), my personal opinion of single vs multi-rail is that it is over hyped.  Power loading is power loading.  It really doesn't matter until you get close to the limit of what the PSU can supply.

 

Multi-rail just basically splits the total output from one power supply into two (and reality, those two share some components, so not even two different supplies).  As long as you spec a PSU that will comfortably handle expected peak demand, it should not matter (and actually be easier to manage).  What "comfortably" means is subjective.  You can likely choose less headroom with a high quality PSU, as it is less likely to do bad things when pushed close to its limits.

[JonathanM]

Single rail means you have less homework to do when researching a specific PSU.

 

The PSU you choose must be capable of supplying the needed amps for 12V and 5V on the lines used for hard drives.

 

Multi rail means full rated current may not be available on the hard drive supply lines, so you must find the current rating for hard drive connections specifically. Part of the rated current may be dedicated to video card supply lines. Doesn't mean that PSU won't work, just means you have to find the specifications for the individual rails.

[kakburken]

6 hours ago, ConnerVT said:

With electrical engineering as my college major, but spending the majority of my life in the digital world (but playing a bit with amateur radio), my personal opinion of single vs multi-rail is that it is over hyped.  Power loading is power loading.  It really doesn't matter until you get close to the limit of what the PSU can supply.

 

Multi-rail just basically splits the total output from one power supply into two (and reality, those two share some components, so not even two different supplies).  As long as you spec a PSU that will comfortably handle expected peak demand, it should not matter (and actually be easier to manage).  What "comfortably" means is subjective.  You can likely choose less headroom with a high quality PSU, as it is less likely to do bad things when pushed close to its limits.

 

6 hours ago, JonathanM said:

Single rail means you have less homework to do when researching a specific PSU.

 

The PSU you choose must be capable of supplying the needed amps for 12V and 5V on the lines used for hard drives.

 

Multi rail means full rated current may not be available on the hard drive supply lines, so you must find the current rating for hard drive connections specifically. Part of the rated current may be dedicated to video card supply lines. Doesn't mean that PSU won't work, just means you have to find the specifications for the individual rails.

 

thanks you wonderful people for explaining it to me. So if I understand correct that means that if I choose a single-rail that is +900w (can handle the max load of 879w at spin-up) I don’t need to check the load for hard drive supply lines? (Not that I know which line is for HDD)

 

 I checked the EVGA supernova g6 1000w and it says it has 105w on the +5V. But the HDDs draws 749w at spin-up. So, that shouldn’t matter then since it’s a single-rail UPS?

[JonathanM]

4 hours ago, kakburken said:

the HDDs draws 749w at spin-up

That sounds like total power, if you look up the specific drive model it should give both 5V and 12V power figures. Typically the 5V inrush current is relatively small, most of the power is needed on the 12V line.

 

4 hours ago, kakburken said:

Not that I know which line is for HDD

If the manufacturer provides that information it would be in the full technical specifications.

[kakburken]

48 minutes ago, JonathanM said:

That sounds like total power, if you look up the specific drive model it should give both 5V and 12V power figures. Typically the 5V inrush current is relatively small, most of the power is needed on the 12V line.

 

If the manufacturer provides that information it would be in the full technical specifications.

Sorry, you kinda lost me there.

im thinking about buying either Seagate Exos X18 18TB or 16TB. Or perhaps Seagate Exos X16 16TB. I might even go lower, to 12TB, but on the same models, depending on price at the moment when purchasing. Also checked some on the WD UltraStar DC HCXXX-models in different sizes. At least those seems to be among the best ones when looking at Price/TB over here. And its those ive checked to get the watt usage at spin-up (took the ones with the highest watt usage, i believe it was the Seagate Exos X18).

 

Though i cant seem to find that information about 5V/12V power figures. Or i dont know what to look for.

 

And im still not sure if i understand it right. you mean the total power isnt something i need to care about for when choosing a PSU so it can handle the spin-up? As far as (i thought) i knew the spin-up was the moment when the most amount of power was used and you "had" to choose a PSU that could handle that amount of wattage, if i dont want to use staggered in unraid. 

 

Sorry if it all sounds dumb, having a hard time grasping what it is need to check for, to be able to have the PSU handle to boot it all up without staggered and just .. well.. power the thing without issues.

 

 

EDIT: i found this about the Seagate Exos X18 (and that is what i used to calculate spin-up power)

 

Startup current (typical) 12V (peak) 2.6A

                                                     2.0A (optional configuration through Smart Command Transport)

 

But as i said, found nothing about 5V.

Edited June 26 by kakburken

[JonathanM]

16 minutes ago, kakburken said:

found nothing about 5V.

https://www.seagate.com/www-content/product-content/enterprise-hdd-fam/exos-x18-channel/_shared/en-us/docs/100865854d.pdf#G4.830176

16 minutes ago, kakburken said:

the spin-up was the moment when the most amount of power was used and you "had" to choose a PSU that could handle that amount of wattage, if i dont want to use staggered in unraid. 

Correct, but the limiting factor is typically the 12V draw, and the PSU total power is all the different voltages combined. When you look at the full spec sheets on a PSU it will list the limits of each voltage separately, as well as the combined total, which is less than adding up each separate feed because they share parts.

 

Part of the issue with communicating all this, you are asking questions that require at least some electronic engineering knowledge to explain the answers. I know you want a simple "how do I know this will do what I want" type of answer, but it's way more nuanced.

 

Some PSU's are designed for heavy draw from the CPU, motherboard and video cards, while neglecting storage. Others provide more balanced output. To figure out which is which, you really have to get into the weeds with the PSU tech specs.

 

12 hours ago, JonathanM said:

Single rail means you have less homework to do when researching a specific PSU.

 

That is the broad generalization glossing over all the nitty gritty details.

 

 

[kakburken]

1 minute ago, JonathanM said:

https://www.seagate.com/www-content/product-content/enterprise-hdd-fam/exos-x18-channel/_shared/en-us/docs/100865854d.pdf#G4.830176

Correct, but the limiting factor is typically the 12V draw, and the PSU total power is all the different voltages combined. When you look at the full spec sheets on a PSU it will list the limits of each voltage separately, as well as the combined total, which is less than adding up each separate feed because they share parts.

 

Part of the issue with communicating all this, you are asking questions that require at least some electronic engineering knowledge to explain the answers. I know you want a simple "how do I know this will do what I want" type of answer, but it's way more nuanced.

 

Some PSU's are designed for heavy draw from the CPU, motherboard and video cards, while neglecting storage. Others provide more balanced output. To figure out which is which, you really have to get into the weeds with the PSU tech specs.

 

 

That is the broad generalization glossing over all the nitty gritty details.

 

 

yes, I understand more knowledge is needed to both explain and understand (since I can’t do neither lol).

 

 But how are we, the ignorant mass, going to be able to choose a PSU that can handle what we want it to handle (like in my case power everything and handle spin-up without staggered) without going back to school?

 

and once again, the last part you added again about single-rail. You still make it sound like if I choose a single-rail I don’t have to check all the details about 5V/12V and just choose a PSU with +900w and it will work fine. And only if I choose to buy a multi-rail I have to check for those specifications. Is that correct or am I (once again) misunderstanding?

 

 If so it seems single-rail is the way to go for me so I can be sure it works.

[JonathanM]

4 minutes ago, kakburken said:

You still make it sound like if I choose a single-rail I don’t have to check all the details about 5V/12V and just choose a PSU with +900w and it will work fine

As long as it's high quality from a good brand, sure.

 

Narrow down your choices to the few that are actually obtainable in your market, and find the tech sheets for those specific supplies. Look for the power rating on the 12V section. Comparing several different models with the same overall rating, choose the one with the higher 12V capacity.

[kakburken]

5 hours ago, JonathanM said:

As long as it's high quality from a good brand, sure.

 

Narrow down your choices to the few that are actually obtainable in your market, and find the tech sheets for those specific supplies. Look for the power rating on the 12V section. Comparing several different models with the same overall rating, choose the one with the higher 12V capacity.

ok, guess ill look thru that list that ConnerVT gave me. though, at a quick glance its a struggle.

Like the single-rail Chieftronic Power Play Platinum 1050W, the specs says:

 

+12V                             183.33A

+12V2                           -

+12V1, +12V2 combined 999.96W

-12V0,                           3A / 3,6W

 

thats a lot of different 12V that i have no clue on which of those i need to look at.

[JonathanM]

35 minutes ago, kakburken said:

thats a lot of different 12V that i have no clue on which of those i need to look at.

Since it's single rail, the only number that matters is the 183.33A.

24 drives X ~3A is around 75A worst case on the 12V hard drive feed. 75A x 12V = 900W.

So, that PSU would have around 150W left available for motherboard, CPU, video and fans during a worst case power demand event. Realistically, that 900W hard drive number will probably never happen in real world, so it should provide plenty of power even when it's a few years old and has some wear on it.

 

So, using back of the napkin rough math, that PSU is a very good candidate.

[kakburken]

14 minutes ago, JonathanM said:

Since it's single rail, the only number that matters is the 183.33A.

24 drives X ~3A is around 75A worst case on the 12V hard drive feed. 75A x 12V = 900W.

So, that PSU would have around 150W left available for motherboard, CPU, video and fans during a worst case power demand event. Realistically, that 900W hard drive number will probably never happen in real world, so it should provide plenty of power even when it's a few years old and has some wear on it.

 

So, using back of the napkin rough math, that PSU is a very good candidate.

Ok, so its the 12V+ number i have to look at? if thats the case, all of the PSU's have the exact same 12V watt as its sold as except a few:

"Adata XPG CyberCore II 1000W", says it has 1300W on the 12V+ (not sure if this correct tho).

"Chieftec PowerPlay Platinum Series 1050W" says it has 1000W.

"Thermaltake Toughpower DPS G RGB 1000W" says it has 996W.

"Thermaltake Toughpower PF1 ARGB 1050W" and "Seasonic TX 1300W" i couldnt find the 12V+ specs.

"Corsair RMx 1000W" had 999.6W

"EVGA G6 Gold 1000W" had 999.6W (83.3A, but they translate that to 1000W in spec sheets)

 

And these had the same 12V+ specs as its sold as:

"Cougar Polar 1050W" had 1050W

"EVGA P6 Platinum 1000W" had 1000W

"MSI A1000G 1000W" had 1000W

"Thermaltake Toughpower GF1 1000W" had 1000W

 

All of them was marked as Tier A (High-End) with yellow text (best in tier). So i guess i could take any of those. Just choose the cheapest ones. 

Edited June 26 by kakburken

[JonathanM]

2 minutes ago, kakburken said:

Just choose the cheapest ones. 

Sure, I'll just throw one more wrench at you.

 

Look for the number and layout of hard drive cables that come stock, along with the ability to source more for the specific model if needed.

 

Modular power supply cables are NOT always interchangeable, sometimes they are, but the consequences if they are not is catastrophic to any attached hard drives. Make sure the power supply you choose either comes with enough connections out of the box, or has availability of the appropriate cables.

 

I'm assuming (perhaps wrongly, but you didn't say) that for 24 drives you are using some sort of backplane arraignment that should make cabling easier, but it would suck to buy a PSU and find out that you can't connect your drives because of a lack of proper cables.

[kakburken]

1 hour ago, JonathanM said:

Sure, I'll just throw one more wrench at you.

 

Look for the number and layout of hard drive cables that come stock, along with the ability to source more for the specific model if needed.

 

Modular power supply cables are NOT always interchangeable, sometimes they are, but the consequences if they are not is catastrophic to any attached hard drives. Make sure the power supply you choose either comes with enough connections out of the box, or has availability of the appropriate cables.

 

I'm assuming (perhaps wrongly, but you didn't say) that for 24 drives you are using some sort of backplane arraignment that should make cabling easier, but it would suck to buy a PSU and find out that you can't connect your drives because of a lack of proper cables.

wow, i have been so occupied with figuring out which PSU i need in regards to watt. so i totally forgot that i actually need to connect it to the hdd's too haha (that or im so used to SSD's so i just didnt think HDD's needed the power connection). thanks for the reminder!

 

im going to buy a Inter-Tech 4724 chassi that has a 6G 2x12-way backplane and if the spec sheet are to be trusted its 3x molex for "electrical connection". Not sure if its 3x for every 12-way (so a total of 6x molex) or 3 in total though. but my guess is that its 3 total.

 

guess that means the PSU needs to have 3 cables for hard drives? And is it "molex 4-pin connector" i have to check for on the PSU?

Like the "Adata XPG CyberCore II 1000W" says:

 

Molex 4 Pin Connector
1000W：4

 

Cable Quantity: 1

 

But it also says some weirdness with the cables length, i think. They say cable quantity "1", but states four different lengths.

 

 

Or perhaps its just so easy that its one cable that has 4 molex on it? i.e the left side of the cable on the image goes to the PSU and it has 4 molex on the other side that goes to the HDDs (in my case the backplane)

 

So, for that PSU it has enough connectors, bu not enough cables? And perhaps even to short if it turns out it is only 15cm long

Am i right in thinking that are the connectors i need to look for?

 

not sure what you mean with the layout of the hard drive cables though?

[JonathanM]

6 minutes ago, kakburken said:

one cable that has 4 molex on it?

exactly, but the spacing isn't likely to match up perfectly with your case.

 

6 minutes ago, kakburken said:

Not sure if its 3x for every 12-way (so a total of 6x molex) or 3 in total though. but my guess is that its 3 total.

3 connectors for 24 drives isn't likely. Probably 6 that need connections.

 

Looks like that specific PSU has 3 connection points for hard drives, so you would want to source 2 more molex style cables for that specific unit and plug each cable into both 12 way bays, so both bays would have power from all three PSU hard drive power connections.

 

Don't even think about trying to run all 24 drives from a single drive power cable.

 

 

[kakburken]

8 minutes ago, JonathanM said:

exactly, but the spacing isn't likely to match up perfectly with your case.

 

3 connectors for 24 drives isn't likely. Probably 6 that need connections.

 

Looks like that specific PSU has 3 connection points for hard drives, so you would want to source 2 more molex style cables for that specific unit and plug each cable into both 12 way bays, so both bays would have power from all three PSU hard drive power connections.

 

Don't even think about trying to run all 24 drives from a single drive power cable.

 

 

 

Ok, so you mean i connect two molex from each cable (three cables) into the 6 slots. so each cable only has two connections going between backplane and PSU?

 

Im not sure how to check if the PSU's ive been looking at has that many slots. Seems the only thing they state in the documentations are how many cables are shipped with the unit, and how many molex connections each cable has. Nothing about how many connectors on the PSU there is for connecting the cables for molex/hdd.

 

Im guessing since they only ship one cable, theres only one connection on the PSU dedicated for power to HDD/Molex?

 

[JonathanM]

Molex / SATA cables should all plug in to the same form connector on the PSU, typically they are just labeled HDD or something like that.

 

Since the PSU you posted comes with 3 total hdd cables, 2 sata and 1 molex, you should be able to order a couple more molex cables and plug them in to the PSU, giving you 3 sets of power feeding your drives. More connections to the PSU = less electrical stress on each connection. You want to divide the load up as evenly as you can across as many wires as you can.

 

Imagine you need to power 6 space heaters. If you plug all 6 into a single power strip plugged into 1 wall outlet, at best you will trip a breaker, worst case you burn the outlet inside the wall. You would want each heater to have its own outlet, with as short a cord as possible.

That scenario is an extreme version of what's going on with your drives.

[kakburken]

2 minutes ago, JonathanM said:

Molex / SATA cables should all plug in to the same form connector on the PSU, typically they are just labeled HDD or something like that.

 

Since the PSU you posted comes with 3 total hdd cables, 2 sata and 1 molex, you should be able to order a couple more molex cables and plug them in to the PSU, giving you 3 sets of power feeding your drives. More connections to the PSU = less electrical stress on each connection. You want to divide the load up as evenly as you can across as many wires as you can.

 

Imagine you need to power 6 space heaters. If you plug all 6 into a single power strip plugged into 1 wall outlet, at best you will trip a breaker, worst case you burn the outlet inside the wall. You would want each heater to have its own outlet, with as short a cord as possible.

That scenario is an extreme version of what's going on with your drives.

 

thanks for that explanation and clarification! 

 

while doing all the browsing, searching, googling, and looking around im pretty sure i read on a few places that its NOT recommended to use any other cables than whats shipped with the PSU (think it was in the context of buying a new PSU and reusing cables from the old/another PSU) or atleast buy the same cables from the same brand that are made for that specific PSU.

 

And it seems i cant find any "acessories cables" for at least the first PSU on my list here, the "Adata XPG CyberCore II 1000W".

Do you mean i can just buy whatever molex cable i want that has the same connector that fits in the PSU? (whatever that connection is)

[JonathanM]

3 minutes ago, kakburken said:

Do you mean i can just buy whatever molex cable i want that has the same connector that fits in the PSU? (whatever that connection is)

NO!!!!!

 

You need to reach out to Adata tech support (or whichever PSU you land on) and get the correct cables. You need 2 more identical to the single molex that comes with the PSU.

 

If that isn't possible or otherwise unlikely, then you will need to educate yourself further on WHY I said what I said earlier, so you can use third party cables safely. It involves checking pinouts, verifying voltages, testing for correct function BEFORE plugging any hard drives into the suspect cables.

2 hours ago, JonathanM said:

Modular power supply cables are NOT always interchangeable, sometimes they are, but the consequences if they are not is catastrophic to any attached hard drives. Make sure the power supply you choose either comes with enough connections out of the box, or has availability of the appropriate cables.

 

 

[kakburken]

24 minutes ago, JonathanM said:

NO!!!!!

 

You need to reach out to Adata tech support (or whichever PSU you land on) and get the correct cables. You need 2 more identical to the single molex that comes with the PSU.

 

If that isn't possible or otherwise unlikely, then you will need to educate yourself further on WHY I said what I said earlier, so you can use third party cables safely. It involves checking pinouts, verifying voltages, testing for correct function BEFORE plugging any hard drives into the suspect cables.

 

 

Sounds like i need to really hope that some of those PSUs has enough cables or that i can buy more of them.

Me learning all that and not making a mistake seems like risky business.

 

if im not mistaken it seems like the "Corsair RMx 1000W" comes with 6 connectors on the PSU for sata & peripherals and ships with 3 cables all having 4 molex each. so that one should work for me without having to buy more cables.

 

 

Atleast the manual states this so i guess its ok to use peripheral connectors on PSU for HDDs on this specific PSU:

"5. Connect the peripheral cables, PCI-Express cables, and SATA cables.

A. Connect the peripherals cables to your hard drive and CD-ROM/DVD-ROM power sockets.

B. Connect the SATA cables to your SATA SSD or hard drive’s power sockets"

Edited June 26 by kakburken

[PSteward]

I bought the Corsair HX Series, HX1200 for my 24 bay server as I was getting issues when all my drives were spun at once. Haven't had an issue since!
The sata backplane was molex powered so dealing with that requires caution, definitely balance it and use good quality cables (OEM + splitters only where required).

[kakburken]

5 minutes ago, PSteward said:

I bought the Corsair HX Series, HX1200 for my 24 bay server as I was getting issues when all my drives were spun at once. Haven't had an issue since!
The sata backplane was molex powered so dealing with that requires caution, definitely balance it and use good quality cables (OEM + splitters only where required).

ok thanks for the suggestion! looks like it has both single-rail and multi-rail. but dont come with enough molex (peripheral) cables? seems it only ships with 2 cables with 4 molex on each. if i want to use 2 molex on each cable i need 1 more cable. 

 

Also seems like an EOL product? atleast over here it seems only one webshop has that PSU and one listed it as "discontinued". it costs around $290 (or 265 EUR or 225 GBP) on the shop that still has it.

[PSteward]

For the unit itself I recommend going big, brand name, check that it fit in your case, and plugs are on the correct side (they vary). I also went with 80+ Platinum but you can do whatever.
As for the cables you likely won't find it all in one box and need to find good 3rd party for the molex adapters, just ensuring that anything you connect to the power supply itself is compatible (pin outs are important), otherwise just molex breakouts should be fine if good quality (even though we wish we could avoid, it's impossible!).

Edited June 26 by PSteward