Warehouse-Scale Computers to Exploit Request-Level and Data-Level Parallelism - Computer Architecture: A Quantitative Approach - page 465

FIGURE 6.19 Google customizes a standard 1AAA container: 40 × 8 × 9.5 feet (12.2 ×
2.4 × 2.9 meters) . The servers are stacked up to 20 high in racks that form two long rows of
29 racks each, with one row on each side of the container. The cool aisle goes down the
middle of the container, with the hot air return being on the outside. The hanging rack struc-
ture makes it easier to repair the cooling system without removing the servers. To allow
people inside the container to repair components, it contains safety systems for fire detection
and mist-based suppression, emergency egress and lighting, and emergency power shut-off.
Containers also have many sensors: temperature, airflow pressure, air leak detection, and
motion-sensing lighting. A video tour of the datacenter can be found at ht-
tp://www.google.com/corporate/green/datacenters/summit.html . Microsoft, Yahoo!, and many
others are now building modular datacenters based upon these ideas but they have stopped
using ISO standard containers since the size is inconvenient.
Cooling And Power In The Google WSC
Figure 6.20 is a cross-section of the container that shows the airflow. The computer racks are
attached to the ceiling of the container. The cooling is below a raised floor that blows into the
aisle between the racks. Hot air is returned from behind the racks. The restricted space of the
container prevents the mixing of hot and cold air, which improves cooling efficiency. Variable-
speed fans are run at the lowest speed needed to cool the rack as opposed to a constant speed.