Hardware Reference
In-Depth Information
hold exactly 80 PCs and switches can be larger or smaller than 128 ports; these are
just typical values for a Google cluster.
OC-12 Fiber
OC-48 Fiber
128-port Gigabit
Ethernet switch
128-port Gigabit
Ethernet switch
Two gigabit
Ethernet links
80-PC rack
Figure 8-44.
A typical Google cluster.
Power density is also a key issue. A typical PC burns about 120 watts or about
10 kW per rack. A rack needs about 3 m
2
so that maintenance personnel can in-
stall and remove PCs and for the air conditioning to function. These parameters
give a power density of over 3000 watts/m
2
. Most data centers are designed for
600-1200 watts/m
2
, so special measures are required to cool the racks.
Google has learned three key things about running massive Web servers that
bear repeating.
1. Components will fail so plan for it.
2. Replicate everything for throughput and availability.
3. Optimize price/performance.
