Hardware Reference
In-Depth Information
Note that if it's too cold outside, the cooling towers need heaters to prevent ice from form-
ing. One of the advantages of placing a WSC in The Dalles is that the annual wet-bulb tem-
perature ranges from 15°F to 66°F (−9°C to 19°C) with an average of 41°F (5°C), so the chillers
can often be turned of. In contrast, Las Vegas, Nevada, ranges from −42°F to 62°F (−41°C to
17°C) with an average of 29°F (−2°C). In addition, having to cool only to 81°F (27°C) inside the
container makes it much more likely that Mother Nature will be able to cool the water.
Figure 6.21
shows the server designed by Google for this WSC. To improve efficiency of the
power supply, it only supplies 12 volts to the motherboard and the motherboard supplies just
enough for the number of disks it has on the board. (Laptops power their disks similarly.) The
server norm is to supply the many voltage levels needed by the disks and chips directly. This
simpliication means the 2007 power supply can run at 92% efficiency, going far above the
Gold rating for power supplies in 2010 (
Figure 6.17
)
.
FIGURE 6.21
Server for Google WSC
. The power supply is on the left and the two disks are
on the top. The two fans below the left disk cover the two sockets of the AMD Barcelona mi-
croprocessor, each with two cores, running at 2.2 GHz. The eight DIMMs in the lower right
each hold 1 GB, giving a total of 8 GB. There is no extra sheet metal, as the servers are
plugged into the battery and a separate plenum is in the rack for each server to help control
the airflow. In part because of the height of the batteries, 20 servers fit in a rack.
Google engineers realized that 12 volts meant that the UPS could simply be a standard bat-
tery on each shelf. Hence, rather than have a separate batery room, which
Figure 6.9
shows
as 94% eicient, each server has its own lead acid batery that is 99.99% eicient. This “dis-
tributed UPS” is deployed incrementally with each machine, which means there is no money
for power spent on overcapacity. They use standard off-the-shelf UPS units to protect network
switches.
What about saving power by using dynamic voltage-frequency scaling (DVFS), which
Chapter 1
describes? DVFS was not deployed in this family of machines since the impact on
latency was such that it was only feasible in very low activity regions for online workloads,
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