Redundancy

Redundancy is the practice of building extra copies of critical parts into a system, such as spare servers, backup power, duplicate network links or copies of data in more than one location, so that the failure of any single part does not stop the service. Engineers aim to remove single points of failure. Banks and payment operators are expected by regulators to maintain redundant sites and tested recovery plans, and many processors use payment failover to switch to a backup route when one fails. Public blockchains achieve redundancy by design: thousands of full nodes each keep a complete copy of the distributed ledger, so no single machine's failure loses data. Redundancy has costs in hardware, storage and coordination, and duplicated systems that share a hidden dependency can still fail together. The word also has an unrelated employment meaning, the loss of a job.