Hardware Reference
In-Depth Information
Example
How long does it take to transfer 1000 MB between disks within the server,
between servers in the rack, and between servers in different racks in the array?
How much faster is it to transfer 1000 MB between DRAM in the three cases?
Answer
A 1000 MB transfer between disks takes:
A memory-to-memory block transfer takes
Thus, for block transfers outside a single server, it doesn't even mater wheth-
er the data are in memory or on disk since the rack switch and array switch
are the botlenecks. These performance limits afect the design of WSC software
and inspire the need for higher performance switches (see
Section 6.6
)
.
Given the architecture of the IT equipment, we are now ready to see how to house, power,
and cool it and to discuss the cost to build and operate the whole WSC, as compared to just
the IT equipment within it.
6.4
Physical
Infrastructure
and
Costs
of
Warehouse-Scale Computers
To build a WSC, you first need to build a warehouse. One of the first questions is where? Real
estate agents emphasize location, but location for a WSC means proximity to Internet back-
bone optical fibers, low cost of electricity, and low risk from environmental disasters, such as
earthquakes, floods, and hurricanes. For a company with many WSCs, another concern is ind-
ing a place geographically near a current or future population of Internet users, so as to reduce
latency over the Internet. There are also many more mundane concerns, such as property tax
rates.
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