Rasberry pi - high density

Tue May 12 03:25:10 UTC 2015

Rather then guessing on power consumption, I measured it.

I took a Pi (Model B - but I suspect B+ and the new version is relatively
similar in power draw with the same peripherials), hooked it up to a lab
power supply, and took a current measurement.  My pi has a Sandisk SD card
and a Sandisk USB stick plugged into it, so, if anything, it will be a bit
high in power draw.  I then fired off a tight code loop and a ping -f from
another host towards it, to busy up the processor and the network/USB on
the Pi.  I don't have a way of making the video do anything, so if you were
using that, your draw would be up.  I also measured idle usage (sitting at
a command prompt).

Power draw was 2.3W under load, 2.0W at idle.

If it was my project, I'd build a backplane board with USB-to-ethernet and
ethernet switch chips, along with sockets for Pi compute modules (or
something similar).  I'd want one power cable and one network cable per
backplane board if my requirements allowed it.  Stick it all in a nice card
cage and you're done.

As for performance per watt, I'd be surprised if this beat a modern video
processor for the right workload.

On Mon, May 11, 2015 at 5:16 PM, Rafael Possamai <rafael at gav.ufsc.br> wrote:

> Maybe I messed up the math in my head, my line of thought was one pi is
> estimated to use 1.2 watts, whereas the nuc is at around 65 watts. 10 pi's
> = 12 watts. My comparison was 65watts/12watts = 5.4 times more power than
> 10 pi's put together. This is really a rough estimate because I got the
> NUC's power consumption from the AC/DC converter that comes with it, which
> has a maximum output of 65 watts. I could be wrong (up to 5 times) and
> still the pi would use less power.
>
> Now that I think about it, the best way to simplify this is to calculate
> benchmark points per watt, so rasp pi is at around 406/1.2 which equals
> 338. The NUC, roughly estimated to be at 3857/65 which equals 60. Let's be
> very skeptical and say that at maximum consumption the pi is using 5 watts,
> then 406/5 is around 81. At this point the rasp pi still scores better.
>
> Only problem we are comparing ARM to x86 which isn't necessarily fair (i am
> not an expert in computer architectures)
>
>
>
>
>
> On Mon, May 11, 2015 at 5:24 PM, Hugo Slabbert <hugo at slabnet.com> wrote:
>
> > Did I miss anything? Just a quick comparison.
> >>
> >
> > If those numbers are accurate, then it leans towards the NUC rather than
> > the Pi, no?
> >
> > Perf:   1x i5 NUC = 10x Pi
> > $$:     1x i5 NUC = 10x Pi
> > Power:  1x i5 NUC = 5x Pi
> >
> > So...if a single NUC gives you the performance of 10x Pis at the capital
> > cost of 10x Pis but uses half the power of 10x Pis and only a single
> > Ethernet port, how does the Pi win?
> >
> > --
> > Hugo
> >
> >
> > On Mon 2015-May-11 17:08:43 -0500, Rafael Possamai <rafael at gav.ufsc.br>
> > wrote:
> >
> >  Interesting! Knowing a pi costs approximately $35, then you need
> >> approximately $350 to get near an i5.. The smallest and cheapest desktop
> >> you can get that would have similar power is the Intel NUC with an i5
> that
> >> goes for approximately $350. Power consumption of a NUC is about 5x that
> >> of
> >> the raspberry pi, but the number of ethernet ports required is 10x less.
> >> Usually in a datacenter you care much more about power than switch
> ports,
> >> so in this case if the overhead of controlling 10x the number of nodes
> is
> >> worth it, I'd still consider the raspberry pi. Did I miss anything?
> Just a
> >> quick comparison.
> >>
> >>
> >>
> >> On Mon, May 11, 2015 at 4:40 PM, Michael Thomas <mike at mtcc.com> wrote:
> >>
> >>  As it turns out, I've been playing around benchmarking things lately
> >>> using
> >>> the tried and true
> >>> UnixBench suite and here are a few numbers that might put this in some
> >>> perspective:
> >>>
> >>> 1) My new Rapsberry pi (4 cores, arm): 406
> >>> 2) My home i5-like thing (asus 4 cores, 16gb's from last year): 3857
> >>> 3) AWS c4.xlarge (4 cores, ~8gb's): 3666
> >>>
> >>> So you'd need to, uh, wedge about 10 pi's to get one half way modern
> x86.
> >>>
> >>> Mike
> >>>
> >>>
> >>> On 5/11/15 1:37 PM, Clay Fiske wrote:
> >>>
> >>>  On May 8, 2015, at 10:24 PM, charles at thefnf.org wrote:
> >>>>
> >>>>>
> >>>>> Pi dimensions:
> >>>>>
> >>>>> 3.37 l (5 front to back)
> >>>>> 2.21 w (6 wide)
> >>>>> 0.83 h
> >>>>> 25 per U (rounding down for Ethernet cable space etc) = 825 pi
> >>>>>
> >>>>> Cable management and heat would probably kill this before it ever
> >>>>> reached completion, but lol…
> >>>>>
> >>>>>
> >>>> This feels like it should be a Friday thread. :)
> >>>>
> >>>> If you’re really going for density:
> >>>>
> >>>> - At 0.83 inches high you could go 2x per U (depends on your mounting
> >>>> system and how much space it burns)
> >>>> - I’d expect you could get at least 7 wide if not 8 with the right
> >>>> micro-USB power connector
> >>>> - In most datacenter racks I’ve seen you could get at least 8 deep
> even
> >>>> with cable breathing room
> >>>>
> >>>> So somewhere between 7x8x2 = 112 and 8x8x2 = 128 per U. And if you get
> >>>> truly creative about how you stack them you could probably beat that
> >>>> without too much effort.
> >>>>
> >>>> This doesn’t solve for cooling, but I think even at these numbers you
> >>>> could probably make it work with nice, tight cabling.
> >>>>
> >>>>
> >>>> -c
> >>>>
> >>>>
> >>>>
> >>>>
> >>>
>