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To continue the discussion of data center power consumption,
I'd like to take a quick look at alternatives for addressing power utilization
by optimizing the hardware side of the problem.
Before I begin, I wanted to share an interesting link with you about the power consumption of each avatar (simulated person) in the online simulation Second Life. I wanted to say it is amusing, but it actually raises worrisome questions about our whole IT infrastructure and who ends up paying these energy costs. The article points out that the average avatar consumes about as much power as a Brazilian citizen. You can read more here. In any case, the article reminded me how important the link is from a company's business model through its software implementation, then through its hardware, then the electricity bill and finally the bottom line that investors will see.
As I mentioned in the first article, power supply efficiency
has a large impact on server power consumption and heat generation. If you are buying servers in small lots,
it's hard to have control over what's inside your servers. For example, the average server power supply
is 65% efficient. Compare this to
Google, which custom-builds their own servers from selected off-the-shelf
components and achieves claimed power supply efficiencies of 90%. In ENKI's data center, we're also building
our own servers to optimize the hardware environment for our business. After optimizing for the cost of physical
space for the server and equipment costs, we don't always have the flexibility
to choose the highest efficiency power supplies. However, whenever possible we choose 80+% efficiency power
supplies. For a 500-watt server, this
translates to a 144-watt reduction, or about a $150 yearly savings (at an
assumed electricity cost of about $0.12 per kilowatt hour.) Recently a number of large vendors including
Dell and IBM have started to deliver servers with power supply efficiencies of
up to 91%, but at a price premium.
Given the inevitable electricity rate increases and the fact that you
will also save on cooling costs, these servers can save you a significant
amount over the life of the equipment.
If you're buying larger quantities of servers, it may make
sense to buy them with DC power supplies which are much more efficient, often
exceeding 90%. A few vendors offer this
option but before you go for it, make sure that you have DC power available and
it is reasonably priced. Many data
centers charge a stiff premium for supplying DC power, including a provisioning
fee. Also, you'll need to rewire your
entire power supply distribution system for the higher currents that
low-voltage DC requires. You'll want to
balance these extra costs against the energy savings! Another option is making your own DC power. Rackable Systems, for example, offers AC-DC
converters (rectifiers) that go in the top of a rack of servers, and supply
redundant DC power to each server.
Rackable claims a total of 30% power savings using this configuration
(implying that their overall power supply efficiency is close to 95%), as well
as increased server reliability because a lot of the waste heat is confined to
the rectifiers in the top of the rack.
Once again, you'll need to sharpen your pencil to determine if the
considerable extra cost of the Rackable solution will save you money during
your planning horizon.
After the power supply, the next largest source of heat in a
server is the processor. Both Intel and
AMD claim to have lower power utilization than the other, and each has an
interesting story to back it up. The
current Intel processors use less power than equivalent-performance AMD chips,
but when you factor in the power from their "chipset" (external support circuitry and memory controller) and
the special FB-DIMM memory they require, AMD's systems may use less power overall. Sun's "Niagara" processor was specifically
designed to save power, and some reviews show it to be three to five times more
efficient than the latest AMD or Intel processors. Between different rating metrics and measurement philosophies
from each processor vendor, it can be hard to tell which will be more
efficient; so many experts recommend that you actually measure the power usage
of each server you are interested in buying under your typical loads to
determine which has the lowest power consumption. We use a "clamp-on" current meter and test our servers with actual application software loads. In general, you can save power by increasing the number of
processor cores in a server, since the power-hungry memory and support
circuitry is shared. Blade systems
offer some of the highest processing power per watt efficiency, but because
of the large number of processors per case, they also draw a lot of power so
you will want to calculate the total power draw per rack before you assume your
current infrastructure can handle the current.
Don't forget that with the large power density of blade solutions, power
supply efficiency becomes even more important.
Finally, there are things you can do to reduce incidental
power consumption from cooling. HP,
APC, EMC, and IBM have thermal management systems and services that can make a
new or remodeled data center more efficient by controlling the amount of
cooling sent to each rack of equipment and hence reducing cooling
requirements. These are expensive
options best applied to an entire large data center, but these vendors claim to be able to save you significant sums. On a smaller scale, Rackable has optimized
cooling in their servers and fully-configured racks containing back-to-back
servers with passive airflow technology. This saves power used to run cooling fans
and reduce temperature variation in your data center by eliminating the
ubiquitous hot aisle/cold aisle layout. Chatsworth Products Inc. has some nice retrofit racks that can do the same thing with your choice of server hardware.
One thing to remember is that data center equipment has a
finite life. Depreciation rules allow
you to set the financial life of a server, and now that
manufacturers understand that power consumption matters, you can expect
increases in computing efficiency to occur regularly over time. Thus, it makes sense to rotate your
equipment through your data center with regular purchases to keep the average
power consumption down, much like a good investor would purchase stock monthly
rather than all at once. This means you
will want to plan for any growth and make arrangements to only purchase what
you need in each period.
In my next article on data center power consumption, we'll
move on to software and systems architecture options to reduce power usage,
including but not limited to virtualization.
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