Power Supply Sizing

[KMR]

Hey Folks,

It's time to upgrade my pool again and I'm thinking my current 450W Seasonic 80+ Gold PSU won't be up to the task (although if it is that would be fantastic).

The server specs are as follows:
14x 7200RPM drives (10 3TB & 4 1TB).
32GB ECC Ram
Xeon 1230v2 CPU
Super Micro MB
2x M1015 HBAs.
3x 120mm fans which are fairly powerful.
2x Intel Dual gigabit NICs.

Will my current PSU survive this workload (usually not very intensive) or should I get a more powerful one?

If my current one is fine that's great, but if I have to get a new one I'd like to get one that will allow me to run a full 24 drives at some point in the future.

Any suggestions?

Thanks,

P.S. I have staggered drive spin up turned on in the MB settings.

 

[SweetAndLow]

Should be plenty of PSU. I think the estimate for drives is 15watts per drive. You could even spin them all up at the same time and be just fine.

 

[Ericloewe]

Simultaneous spinup is cutting it a bit close, especially with 7200 RPM drives. It *should* manage, but if behavior is wonky, replace it with a larger unit.

 

[KMR]

I have staggered spin up set in the motherboard settings.. but would that also work for the drives connected to the M1015's?

 

[Ericloewe]

I have staggered spin up set in the motherboard settings.. but would that also work for the drives connected to the M1015's?

It's always rather hard to determine if it'll work. You pretty much would have to figure that out by yourself. Most people just size the PSU based on spinup current.

 

[hertzsae]

The staggered spinup in the motherboard bios should only be for drives connected to it. The M1015 may have its own setting for staggered spinup.

Also, the 7.2K Hitachi drives that I have are listed at 30 Watts, so I'm not sure where the 15 Watt estimate comes from.

From the spec sheet - "Startup current (A, max.) (1.2A, max +5V, 2A @ +12V)"
For those that don't know electricity, you multiply the Amps by the volts and add them up:
1.2 A * 5 V = 6 Watts
2A * 12V = 24 Watts
6 + 24 = 30 Watts total per drive or 420 Watts for 14

You'd also want to check the specs on the PSU to make sure it had enough 5V and 12V power. If your drives were the same, you'd need
14 drives * 6 W = 84 W at 5V
14 d * 24 W = 336 W at 12V

 

[Glorious1]

Interesting. Unfortunately it seems not all drives have spinup power in the spec sheets. For instance, the WD Red NAS drive spec sheet only gives power needs for read/write, idle, and standby/sleep.

 

[rogerh]

Interesting. Unfortunately it seems not all drives have spinup power in the spec sheets. For instance, the WD Red NAS drive spec sheet only gives power needs for read/write, idle, and standby/sleep.

It is inappropriate to use spinup power in sizing a power supply, especially if the drives are all starting at the same time. The spinup current only occurs for a very short time, not long enough to affect the power suppy's sustained power rating, as long as the peak current from the 12v supply is within the rating for the power supply for 12v peak current. This is why power supplies tend to have a peak current rating that would exceed their power capacity if it was sustained. The document you quote does give the spinup current, 1.75 for the 4TB, which if it were sustained would amount to 21 watts. If spinup is staggered, then power used during spin up may be over a long enough time to be significant.

Using the power of 21W per drive should certainly give a safe and conservative power rating.

Edit: some may object that my power calculation from voltage and current is not precise, because it does not allow for inductive current. That is so, but doesn't affect the above argument.

 

[Glorious1]

Ah, I see, thank you rogerh. I didn't recognize that the peak current draw must be spinup. Makes sense now, also the fact that it makes a very conservative estimate of PSU needs.

 

[hertzsae]

I should have made it more clear that I was only talking about spinup power, which I use a safe overly conservative estimate. I looked up Seagate drives and the 4TB NAS drives list 2A at 12V or 24 W max. Both WD and Seagate don't give a max on the 5V rail, or give a max spinup wattage, so I can't tell if they use more than just their 12V rail during spinup.

 

[rogerh]

My slightly educated guess is that they either don't use the 5V rail at all, or only for the electronics which will be a low and fairly constant power. More during activity than spinup. I could find out (with a DC current clamp meter) but for my own purposes I am happy to assume this.

 

[marbus90]

2A on 12V should be worst case scenario per 3.5" bay with 5400rpm drives. 24 bays would need 48A@12V alone, which is cutting it close even at (for example) Corsair 650W PSUs. I won't bet on Staggered Spinup.

HGST He drives do pull another ~2A on the 5V rail, if using other models than 5400rpm Reds I'd factor that in too.

 

[rogerh]

Yes, sorry I am only talking about the WD Reds and Greens, whose specs say nothing about 5V rails (except for the laptop versions).

 

[Ericloewe]

The old Greens had more detailed data, which sustained the (crude, but very conservative) 30W per drive rule.

My calculations always assume the following:

• PSU is a modern design with DC-DC for the minor rails
  • It can deliver essentially full power just on the 12V rail(s)
  • Its minor rails (5V) can handle whatever small percentage of those 30W is drawn from them
• 5400 RPM HDDs are similar to the late-2012/early 2013 WD Greens, which had detailed specs
• A typical Haswell system won't need more than 60W at startup
• Crazy fans are accounted for separately

With these simplifications, you get the conservative estimates I've been spreading around for half a year without a proper justification.

 

[KMR]

Here is a link to the specs on the drives. 10 are the 3tb model and 4 are the 1tb model:
http://images.anandtech.com/doci/5042/Screen Shot 2011-11-01 at 1.20.26 AM.png

Given that information would it still be safe to try with my current PSU (Seasonic SSR-450RM)?

Thanks,

 

[hertzsae]

The major thing that must be kept in mind is that using 14 drives with a consumer PSU is not normal. This is an outlier system when it comes to power demands. The consumer PSU makers assume that their customers with high wattage needs will be driving big cpus, a handful of hard drives (like 6 max) and a few SLI high power graphics cards. Those gfx cards will be primarily 12V, so it is safe to assume that power supply makers make their high wattage consumer PSUs to be very 12V biased. In fact, most consumer PSUs can probably take the full wattage rating on the 12V rail. The same can not be said for the 5V rail. It looks like the full line of Seasonic G series PSUs from 360W to 650W put a max spec for the 5V rail at 100W (link to spec sheet at the bottom).

So if KMR's drives use 6W on the 5V rail like mine during spinup (assuming staggering doesn't on M1015s), then KMR will need 84W on the 5V rail just for drives. If they are like the HGST He drives (10W), KMR will need 140W at 5V during spinup. In both cases, there is either zero or very little headroom in the listed psu spec for all the other components in the system that use 5V. Since WD doesn't list a 5V spec, it's also possible that they don't use any 5V during spinup and this argument is mute.

Now we all know that specs are meant to be broken and that we can exceed them at that times with no consequences. However, I wouldn't be surprised if the 5V rail dips more than it should if we put more than 100W on it. Will the other components have problems with an undervoltage? For the brief duration, probably not, but I can't say with certainty.

In summary:
Would I trust it with a home system? Probably. Would I trust it for my business, absolutely not. If this system's uptime is critical, then get a server PSU that is built for many hard drives and stay away from the consumer ones with their smaller 5V spec.

http://www.seasonic.com/pdf/datasheet/NEW/Retail/G-650-550-450-360.pdf

 

[hertzsae]

KMR,
That link does not specify 5V specs. It just says 2.0 Amps. Is that 2A all on the 12V rail? Is there any on the 5V rail? Most people don't have to worry about it, because they don't have 14 drives. You may want to email Seagate and find out.

 

[KMR]

Unfortunately that is the only information that seems to be available online from the manufacturer.

 

[hertzsae]

Unless you reach out to Seagate, we will be speculating. Is this for a home or mission critical business NAS? You will definitely be fine while operating (8W/drive average) and if staggered works, you will be fine during boot or wakeup. If it's a home box, then just try it out. If its a mission critical NAS, then get a server spec'd PSU.

 

[KMR]

This is for a home box. If I run it and it's not enough what sort of behavior can I expect? Is it dangerous to run it like this?