rack power question

> Would someone pay extra for > 7KW in a rack? What would be the maximum you
> could ever see yourself needing in order to power all 42U ?

As you recognize, its not an engineering question; its an economic
question. Notice how Google's space/power philosphy changed between
leveraging other people's space/power, and now that they own their own

Existing equipment could exceed 20kW in a rack, and some folks are
planning for equipment exceeding 30kW in a rack.

But things get more interesting when you look at the total economics
of a data center. 8kW/rack is the new "average," but that includes
a lot of assumptions. If someone else is paying, I want it and more.
If I'm paying for it, I discover I can get by with less.

That may not be the correct way to look at it.

There's a very reasonable argument to be made that the artificial economic
models used by colocation providers has created this monster to begin with.

The primary motivation for many customers to put more stuff in a single
rack is that the cost for a rack subsidizes at least a portion of the power
and cooling costs. A single rack with two 20A circuits typically costs less
than two racks with a 20A circuit each. To some extent, this makes sense.
However, it often costs *much* less for the single rack with two 20A

Charging substantially less for rack space, even offset by higher costs for
power, would encourage a lot of colo customers to "spread the load" around
and not feel as obligated to maximize the use of space. That would in turn
reduce the tendency for there to be excessive numbers of hot spots.

The economic question of how to build your pricing model ultimately becomes
an engineering question, because it becomes progressively more difficult to
provide power and cooling as density increases.

Or, to quote you, in an entirely different context:

If I'm paying for it, I discover I can get by with less.

The problem is that this is currently true for values of "it" where "it"
equals "racks."

... JG

I wonder if we're to the point yet where we should just charge for power
and give the space away "free"....

When I'm shopping for colo that's pretty much the way I look at it. Power determines space. I need 80,000W of power at the breaker, so I need 800sqftx15$ in facility A, and 320sqft@40$ in facility B.

I can fit my 8 racks into either the 320sqft or into the 800. If I'm doing the 800, I'll probably spend a bit more up front and use 12 or 14 racks, to keep my density down. A bit more cost up front, but in the grand scheme of things 4 or 6 extra racks ($6 to 10,000$) don't directly hurt to much. (80kW worth of power usually means you've got well north of $2M worth of hardware and software being stuffed into the space in my experience..but maybe that's because we're an Oracle shop. :wink:

Of course, I suppose for those customers still doing super-low-density boxes (webhosting with lots and lots of desktops), I suppose that model wouldn't work as well.



Basically, that is the state of things. You’re paying for power (which is also cooling) and bandwidth/connectivity.

Globix is only letting us run one 30A 240V circuit per rack for “cooling reasons”, however even with our 6850s we manage to populate a good portion of the rack. However, this means that for redundancy we cannot put anyone’s partner in crime in the same cabinet. Though Globix is the typical cold-in-front, hot-in-back setup they still seem to be under-capacity when it comes to cooling… I think the end of the dot-com boom put a dent in their Liebert budget. It amazes me places like Hurricane can’t get enough space when there are once-decent shops like Globix with so much unused space.

Plan your power requirements carefully, and plan on the ability to upgrade in the future. With the current trend of high-capacity blades, it seems that it would not be impossible to find 20-25kw per cabinet not long from now. Power distribution (if done right) is easy, cooling that density is the fun part. What’s your cooling plan?


There's at least one small example of someone doing that already.