Question on how to best power 72 2.5" SATA SSD/Hard drives

[davidhewitt128]

I’m planning of setting up a file server and will be using 72 2.5” drives and having a few concerns about powering them.

I have done some rough estimations on power consumption:
http://www.seagate.com/www-content/datasheets/pdfs/mobile-hddDS1861-2-1603-en_GB.pdf
~2W per drive load: 2 * 72 = 144W

http://www.anandtech.com/show/8747/samsung-ssd-850-evo-review/10
Some use up to 4W.
Due to the planned use of SAS Expanders the maximum data bandwidth of each drive will be significantly reduced so lets say a more generous maximum power consumptions of 3W per drive.
3 * 72 = 216W

Interesting that SSDs have higher load power consumption but their idle is much lower in the mW range vs about half a Watt.

For 2.5” drives it looks like the 3.3V and 12V rails are never used looking at the data sheets of a few drives, so only the 5V rail is needed. I was planning on using a Seasonic Prime 750W power supply but the 5V rail can only provide 100W, when I need more than double just for drives not to mention the motherboard’s need for 5V.


There is plenty of power on the 12V rail and I’m wondering if using two 12V to 5V DC-DC would be solution to this problem.
Looking at this converter http://www.current-logic.com/shop/index.php?main_page=product_info&cPath=4&products_id=179 The manufacture says not to run >80% continuously for more than 30 minutes. I plan to run it continuously with fan cooling if needed so I should really consider this to be a 120W unit. Two would provide 240W of power and if at full continuous load at 90% efficiency would draw 267W from the 12V rail.

I was thinking of using a cable like this: https://www.moddiy.com/products/Corsair-Style-8-Conductor-Flat-Ribbon-Cable-Wire-%2818AWG-Black%29.html but it is only 18AWG.

According to this site http://www.solar-wind.co.uk/cable-sizing-DC-cables.html 18AWG can only handle 5V 2A at 50cm. So I’ll need 1 cable per 3 drives?


This drives will be in banks of 8 and 1 set of 4 per DC-DC converter.

Is this a good approach? Any better ideas and how is my logic thanks?

[Codebird]

Very few SATA drives require the 3.3V rail, for the simple reasons that most desktops don't supply it.

Even 100W at 5V is going to be 20A - at that sort of current you are going to have to use rather thick wiring just to avoid the drives on the end getting a voltage drop due to resistance in the path. You might be better using smaller buck converters, perhaps one per bank of eight or sixteen drives.

[BravoV]

Apart from powering while they're running, also consider staggered spin up if your controller supports it, that will relieve the power on stress at the power supply.

[davidhewitt128]

Thanks, I like the idea of using several smaller buck converters. The smaller 3-5A ones don't seem to need any additional cooling and mounting them easier.

Yes the HBA does support staggered spin-up.

[mycroft]

Maybe this https://www.backblaze.com/b2/storage-pod.html will inspire you.

[davidhewitt128]

I have done some rough estimations on power consumption:
http://www.seagate.com/www-content/datasheets/pdfs/mobile-hddDS1861-2-1603-en_GB.pdf
~2W per drive load: 2 * 72 = 144W

im guessing you want to save power, if so, i think multiple converters will waste more power. a single seasonic (gold?) will be better solution. at low current, individual small converters do not operate efficiently.
http://www.hardwaresecrets.com/seasonic-x-series-750-w-power-supply-review/7/

Are you saying replace the main power supply with the one you suggested? It can output 125W on the 5V rail which is more than than the original one but still not enough. The original is 80 Plus Titanium rated.

I will ask the manufacturer of the buck converters about their efficiency curves.

I don't know if I it's wise to have mixed gauges of wire if I have few larger converters versus many small.

Option 1:
2 x 120W DC-DC: ----5V 24A 10 AWG?-----Splitter|----18 AWG ---- Hard Drive 1
                                               |----18 AWG ---- Hard Drive n
                                               |----18 AWG ---- Hard Drive 35


Option 2:
9 x 25 DC-DC: ----5V 5A 18 AWG?-----Splitter|----18 AWG ---- Hard Drive 1
                                            |----18 AWG ---- Hard Drive n
                                            |----18 AWG ---- Hard Drive 8

Option 3:
Could have 4 x DC-DC.

[Nusa]

I'd leave the ATX to it's original purpose and other peripherals. Skip all the converting and just add a single-voltage 5V supply for the SSD array. A Meanwell 5V 300W supply should be in the $60 neighborhood, which may be cheaper as well as cleaner than what you're planning.

[meeko]

Typically, a server that can take 72x 2.5" drives uses redundant hot-swappable power supplies, which usually just put out 12V at 60+ amps and a 5V standby supply, leaving it to DC-DC converters on the power distribution board (or sometimes right on the motherboard) to divvy that up between the various voltages required.

[cyberfish]

Interesting that SSDs have higher load power consumption but their idle is much lower in the mW range vs about half a Watt.

They are also much faster however. So if the amount of I/O you have to do is constant, SSDs will probably still end up being more power-efficient, because they won't stay active for long.

But they do take more power to read at 500+MB/s vs a 2.5" hard drive at ~100MB/s.

[CJay]

I'm not sure I'd want that much data running on a lashup, have you considered hunting down a couple of storage shelves or expansion unit, something like a HP MSA70 or equivalent?

Apart from the reliability of having a dedicated shelf with it's own power, you may be able to get much higher data rates if it's got its own smarts.

[picandmix]

I like the idea of using several smaller buck converters. The smaller 3-5A ones don't seem to need any additional cooling and mounting them easier.

Think many of those small converters do say you need additional heat sinks if operating above 3A.

Also no mention in your calculations about psu overhead; running any psu at its maximum output will shorten its life / need extra fan cooling.

Would suggest you run at a maximum of 2/3 its rated output, even lower for some of the cheap ebay psus where quality is not known.;  though surely you need supplies of good quality for such a key function.

As said, you do need a decent housing that also allows for effective fan cooling  .