Glossary
PUE, SLA, UPS, Tier, free cooling… datacenter vocabulary explained simply.
Cold aisle: an enclosed corridor in front of the racks where cold air is contained, so it doesn't mix with hot air.
42U rack: the standard cabinet that holds the servers. One unit (U) is 4.45 cm; a rack has 42 of them.
BESS: Battery Energy Storage System, site-scale battery energy storage.
Chiller / CRAC: cold production unit / Computer Room Air Conditioner.
DE-CIX: the Frankfurt Internet exchange point, one of the largest in the world.
Free cooling: cooling that uses cold outside air or water instead of compressors.
HFT: High-Frequency Trading, which demands minimal latency.
KVM: a console used to control servers remotely (Keyboard, Video, Mouse).
kVA / kW: units of electrical power (apparent / active).
N+1: redundancy where one backup unit is added to the N required.
NOC: Network Operations Center, the monitoring center.
OPEX: recurring operating expenses (energy, salaries, rent…).
PaaS: Platform as a Service, managed cloud services (databases, cache…).
PDU: Power Distribution Unit, the rack's smart power strip.
PUE: Power Usage Effectiveness, the site's total energy divided by the IT energy. 1.0 is the theoretical ideal.
SLA: Service Level Agreement, an uptime commitment to a client (for example 99.9%).
SRE: Site Reliability Engineer.
Tier I to IV: the Uptime Institute's availability certification levels, from basic infrastructure to the fault-tolerant datacenter.
UPS: Uninterruptible Power Supply.
vGPU: a virtual GPU shared between several clients.