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ligible performance impact. (Note that such optimizations do not impact PUE but do re-
duce overall WSC energy consumption.)
WSC design must have improved in the intervening years, as Google's best WSC has dropped
the PUE from 1.23 for Google A to 1.12. Facebook announced in 2011 that they had driven PUE
down to 1.07 in their new datacenter (see
htp://opencompute.org/
). It will be interesting to see
what innovations remain to improve further the WSC efficiency so that we are good guardians
of our environment. Perhaps in the future we will even consider the energy cost to
manufacture
the equipment within a WSC [
Chang et al. 2010
].
6.8 Fallacies and Pitfalls
Despite WSC being less than a decade old, WSC architects like those at Google have already
uncovered many pitfalls and fallacies about WSCs, often learned the hard way. As we said in
the introduction, WSC architects are today's Seymour Crays.
Fallacy Cloud Computing Providers Are Losing Money
A popular question about cloud computing is whether it's profitable at these low prices.
Based on AWS pricing from
Figure 6.15
, we could charge $0.68 per hour per server for com-
putation. (The $0.085 per hour price is for a Virtual Machine equivalent to one EC2 compute
unit, not a full server.) If we could sell 50% of the server hours, that would generate $0.34 of
income per hour per server. (Note that customers pay no mater how litle they use the servers
they occupy, so selling 50% of the server hours doesn't necessarily mean that average server
utilization is 50%.)
Another way to calculate income would be to use AWS
Reserved Instances
, where customers
pay a yearly fee to reserve an instance and then a lower rate per hour to use it. Combining the
charges together, AWS would receive $0.45 of income per hour per server for a full year.
If we could sell 750 GB per server for storage using AWS pricing, in addition to the com-
putation income, that would generate another $75 per month per server, or another $0.10 per
hour.
These numbers suggest an average income of $0.44 per hour per server (via On-Demand In-
stances) to $0.55 per hour (via Reserved Instances). From
Figure 6.13
,
we calculated the cost
per server as $0.11 per hour for the WSC in
Section 6.4
. Although the costs in
Figure 6.13
are
estimates that are
not
based on actual AWS costs and the 50% sales for server processing and
750 GB utilization of per server storage are just examples, these assumptions suggest a gross
margin of 75% to 80%. Assuming these calculations are reasonable, they suggest that cloud
computing is profitable, especially for a service business.
Fallacy Capital Costs Of The WSC Facility Are Higher Than For The Servers That It
Houses
While a quick look at
Figure 6.13
on page 453 might lead you to that conclusion, that glimpse
ignores the length of amortization for each part of the full WSC. However, the facility lasts 10
to 15 years while the servers need to be repurchased every 3 or 4 years. Using the amortiza-
tion times in
Figure 6.13
of 10 years and 3 years, respectively, the capital expenditures over a
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