PSU for 12 drives

[Spearfoot]

 

[raid40000]

yeah sorry, I expected that somehow. I have insisted a bit much on my position and I am sick of it myself but I tried to put the reasoning behind it versus a plain: get 2Kw that will handle it (because some people may have 24 disks or more or want to save money).

For anyone else TL;DR so this thread is helpful:

- disk spin-up matters, if your 500W PSU was about right, then get +200W extra and always get a tier 1 PSU even if it has some hundred less W than a random model.

- try to enable staggered spin-up (not all the hardware supports it). It would be wise to make sure you can enable it. It avoids spikes during boot, which avoids issues with your power supply,etc. For example: PUIS for some WD drives.

- Except during boot, drives would normally use 4W depending on the model. During boot you can expect 1.72A*12V or more for each drive.

- To measure the spike with precision you totally need an oscilloscope as a regular "power meter" will not help. Also many online web tools to give estimates do not consider the spin-up for many hard drives during boot.

 

[Ericloewe]

During boot you can expect 1.72A*12V or more for each drive.

@Bidule0hm measured WD Reds, which aren't exactly known for being power-hungry, at 2.5A per drive.

From there, reasonable sizing is 30W per drive, plus whatever the rest of the system needs. Notice that this is in line with the sizing Supermicro uses in its chassis.

 

[Bidule0hm]

- Get a decent PSU, allow for some W margin but most important make sure you pick a Tier-1 PSU from a reputable make. Else throwing watts on it will not cut it and you can experience a failure over the long run either way.

Yes, I agree.

- And always get hardware that supports for staggered spin-up, so even if you have 4 drives and more than enough wattage there is no need to stress the PSU and cause spikes in power.

The problem with SSU is that the day it doesn't work you'll have all the drives spinning-up at the same time and if you selected the PSU relying on the fact that SSU will always work then you'll have a problem...

- If you have serious availability requirements: get a redundant PSU.

Nothing to do with the subject but, yes.

In my particular case the 500W, being honest, I do not think are surpassed during spin-up and as per the basic maths... the time will tell if it will 'explode' or not, but I feel confident than a random PSU 750W with the same cost as the one I got would eventually 'blow up' equally.

Well, 12 * 35 = 420 so that leaves only 80 W for the system. Then you'll have the PSU wear so you need to derate it because a 5 years PSU will have 44 kh and capacitors are usually in pretty bad shape at 44 kh... so a 80 % derating for example will mean you're at 420 + 420 * 0.2 = 504 W so just with the drives you maxed out the 500 W PSU... So basic maths are actually proving you wrong.

//

The difference between theory and practice is greater in practice than in theory.

A brand new, freshly-lubricated, perfectly temperature balanced hard drive on the test bench draws fewer watts than an older hard drive with dried-up lubricant that has been repeatedly temperature-cycled.

A drive that spins up just fine on day one at 1.5 amps may not spin up with three amps after a couple years.

You came here for expert advice and the experts say 750 watts will give you the greatest chance of success. That said, you're not going to hurt my feelings if you want to use a 400-watt power supply.

I'm more worried about the PSU wear than the drives wear but yeah, same idea: derating.

//

It should. You purchased the wrong PSU otherwise, even if you got way more wattage it was still a far worst purchase.

Nothing to do with the PSU here, he talks about the drives.

The current level of electronics will not simply move from requiring 1.72A to suddenly 3A or else a modern graphic card would burn whole the computer after 5 years.

There's a big difference between a static electronic thing like a graphic card and an electronic + mechanical thing (so moving parts that'll wear with time).

Saying "go for 750W instead of 500W" is something I can understand but it is not that simple and IMHO it is better to go for a tier 1 500W than a tier 2 or tier 3 random PSU on 1000W instead. Over the years the 1000W will fail, the other one will not. (A PSU that will be running 90% of the time under 50% of the max wattage will not fail because two or three random spikes in power unless you truly under-size the PSU.)

We aren't saying that, ever. We are saying a 750 W tier 1 PSU will be better than a 500 W tier 1 PSU.

I believe recommending hardware that supports staggered spin-up is probably a better general advice, regardless of the PSU that you have.

Yes, of course, just don't rely on it for the system to work properly, it's more a nice to have thing.

- disk spin-up matters, if your 500W PSU was about right, then get +200W extra and always get a tier 1 PSU even if it has some hundred less W than a random model.

- try to enable staggered spin-up (not all the hardware supports it). It would be wise to make sure you can enable it. It avoids spikes during boot, which avoids issues with your power supply,etc. For example: PUIS for some WD drives.

- Except during boot, drives would normally use 4W depending on the model. During boot you can expect 1.72A*12V or more for each drive.

- To measure the spike with precision you totally need an oscilloscope as a regular "power meter" will not help. Also many online web tools to give estimates do not consider the spin-up for many hard drives during boot.

That's more like it ;)

//

@Bidule0hm measured WD Reds, which aren't exactly known for being power-hungry, at 2.5A per drive.

From there, reasonable sizing is 30W per drive, plus whatever the rest of the system needs. Notice that this is in line with the sizing Supermicro uses in its chassis.

Yep, exactly ;)

 

[adrianwi]

Well, after this recent thread and jgreco's PSU Sizing thread nagging at my conscious, I eventually caved in an upgraded my Seasonic G450 to a Seasonic 660XP2.

I've removed 2 USB sticks and installed a SSD for boot, but it actually appears to be drawing less power at idle - 80-90 compared with 110-120 - than the old PSU and I can stop worrying about peak load when I have to reboot the machine.

Anyone want to buy a ~12 month old G450 :D