Hardware Reference
In-Depth Information
You could run any workload in any place and optimize for server utilization rather than net-
work traic locality. The WSC network botlenecks today constrain data placement, which in
turn complicates WSC software. As this software is one of the most valuable assets of a WSC
company, the cost of this added complexity can be signiicant.
For readers interested learning more about switch design, Appendix F describes the issues
involved in the design of interconnection networks. In addition, Thacker [2007] proposed bor-
rowing networking technology from supercomputing to overcome the price and performance
problems.
Vahdat et al. [2010]
did as well, and proposed a networking infrastructure that can
scale to 100,000 ports and 1 petabit/sec of bisection bandwidth. A major benefit of these novel
datacenter switches is to simplify the software challenges due to oversubscription.
Using Energy Efficiently Inside The Server
While PUE measures the efficiency of a WSC, it has nothing to say about what goes on inside
the IT equipment itself. Thus, another source of electrical inefficiency not covered in
Figure
6.9
is the power supply
inside
the server, which converts input of 208 volts or 110 volts to the
voltages that chips and disks use, typically 3.3, 5, and 12 volts. The 12 volts are further stepped
down to 1.2 to 1.8 volts on the board, depending on what the microprocessor and memory re-
quire. In 2007, many power supplies were 60% to 80% efficient, which meant there were great-
er losses inside the server than there were going through the many steps and voltage changes
from the high-voltage lines at the utility tower to supply the low-voltage lines at the server.
One reason is that they have to supply a range of voltages to the chips and the disks, since they
have no idea what is on the motherboard. A second reason is that the power supply is often
oversized in wats for what is on the board. Moreover, such power supplies are often at their
worst efficiency at 25% load or less, even though as
Figure 6.3
on page 440 shows, many WSC
servers operate in that range. Computer motherboards also have voltage regulator modules
(VRMs), and they can have relatively low efficiency as well.
To improve the state of the art,
Figure 6.17
shows the
Climate Savers Computing Initiative
standards [2007]
for rating power supplies and their goals over time. Note that the standard
speciies requirements at 20% and 50% loading in addition to 100% loading.
FIGURE 6.17
Efficiency ratings and goals for power supplies over time of the Climate
Savers Computing Initiative
. These ratings are for Multi-Output Power Supply Units, which
refer to desktop and server power supplies in nonredundant systems. There is a slightly high-
er standard for single-output PSUs, which are typically used in redundant configurations (1U/
2U single-, dual-, and four-socket and blade servers).
In addition to the power supply,
Barroso and Hölzle [2007]
said the goal for the whole serv-
er should be
energy proportionality
; that is, servers should consume energy in proportion to the
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