Having more than one of things.
WHAT REDUNDANCY MEANS
A second of something, so a failure does not stop service.
WHERE IT APPLIES IN A FACILITY
Power feeds Generators Cooling units Network connections Equipment power supplies
WHAT THE COMMON NOTATION MEANS
Enough capacity plus one spare Two complete independent systems
WHY THAT DISTINCTION MATTERS
One spare protects against a single failure.
Two complete systems allow maintenance of one while the other runs.
WHAT SINGLE POINTS OF FAILURE ARE
Anything whose failure stops everything.
WHAT TO LOOK FOR
A single power path A single cooling system A single network provider A single route into the building
WHY THAT LAST ONE
Two fibre connections entering through the same duct fail together.
WHAT TO ASK ANY PROVIDER
What happens when each component fails.
WHAT TO ACCEPT
Redundancy adds cost and complexity, and is not always warranted.
