Redundancy is the practice of providing duplicate or spare components, such as servers, disks, power supplies and network links, so that if one fails another can take over.
Why it matters
No component lasts forever, so reliable systems assume failure. Redundancy removes single points of failure: RAID mirrors disks, dual power feeds protect racks, and multiple servers sit behind a load balancer.
More copies cost more and add complexity. Redundancy is also not a backup: if data is deleted or corrupted, a redundant system may copy that damage immediately.
Example
A site runs two web servers in different availability zones, a database with a replica, and two internet providers at the office. Any single item can fail without taking the service offline.
Common misconceptions
- Treating RAID or replication as a replacement for backups.
- Having two copies that share one hidden dependency, such as the same power circuit or provider.
- Not monitoring the spare, so it silently fails and nobody notices until needed.
Related
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