[MLB-WIRELESS] OT: Green community datacentre

[Fenn Bailey]

'lo all,

> 
> Sorry, I'm loosing track o what we are doing here...
> 
> is the aim to provide cheap (near free) 
> community-user-group-based datacentre.
> Or
> provide green-powered same as above?
> 

Well, I certainly can't speak for the list, but I can speak for the original
intent of the email :) The original aim was neither, it was to provide an
affordable, more flexible datacenter (ie: self maintainable machines, etc)
leveraging off recent price drops in connectivity/data and ideally using
(some elements) of green power.

I don't think near-free or entirely green is an achievable goal currently
(sadly).

--snip--
> we seem to have 3 issues identified.
> 
> 1) cost of infrastructure.

Hopefully the bulk of it would be user-contributed (perhaps with a
valuation/rebate scheme if so desired), and any extraneous items that need
to be purchased could be shared.

> 2) how to get enough power into a building to support an 
> arbitrary number of racks.

I was thinking relatively small numbers (initially), with room to grow. So,
based off original email:

 - 10 - 15 "customers"
 - Each customer has 2-3 machines.
 - Each machine draws 300-400W.

So: 

Each customer draws 600W - 1200W, meaning a power requirement (not counting
cooling) of 6kW to 18kW.

This is approximately 75A @ 240v peak draw, which is highish, but
achievable. Keep in mind, the PSU's would rarely all be at the upper end of
the scale and all drawing maximum draw (an overload situation), but would
average no higher than 75% unless something was very wrong, so average power
requirement of 6kW/18kW = 12kW. Let's ignore the utilization clause and put
that in as a safety margin. 

> 3) how to effectively cool the racks. refer to point 2 and 1.
> 

Excellent question. I like using "natural" cooling at times of the year that
it's available. I have no real idea how to calculate this sort of stuff, but
a quick bunch of sums based on: 
http://www.openxtra.co.uk/articles/calculating-heat-load.php

Ignoring room/etc (let's assume it's well insulated, etc, etc - I'm lazy,
someone else can do it properly :):

Room: 5m * 6m * 337 = 10110BTU (quite a big room)
12000 * 3.5 = 42000BTU
Total: 52110BTU

Cooling requirements = 15kW cooling capacity.

According to: http://www.energyrating.gov.au/appsearch/air_srch.asp

2 * MSC-24CRN1-QC1P would give us enough cooling capacity with a combined
draw of 4.4kW.

Now, for electricity COSTS (the scary bit):

Let's assume we can get cheapish electricty rates that average at 9c/kWh.

Average draw of equipment would be 12kW, so 108c/hr or $777/month or
~$62/month/customer.
Aircon draw would vary based on external temperature, day/night/etc. 
Over a year, we'll take a worst case scenario and assume 90% utilization of
aircon, so:

4.4kW * 0.9 * 9c = 35.64c/hr or $256/month or $20.50/customer.

SO! V. guestimated results:

$82.50/month for electricity. Users can be charged per-use to encourage
energy/heat efficient machines, so could be a lot lower utilizing more
heat/energy efficient hardware.

This is (high-ish), but not prohibitive. Remember, you still pay these costs
at home for your home PC as well.

It is very, very likely that half the calculations there are completely
incorrect. I'm no datacentre designer or airconditioning/electrical
engineer, but the exercise is interesting nonetheless.

Thoughts/comments welcome.

	Fenn.