noun
redundant system
Technical term in engineering and IT for a system, string, or line that provides redundancy, often for fault tolerance or reliability.
このネットワークは冗長系を備えているので、一部が故障しても通信が途切れない。
This network has a redundant system, so communication won't be interrupted even if part of it fails.
冗長化 is the process of making something redundant, whereas 冗長系 is the resulting redundant system itself.
Compound of 冗長 (redundancy) and 系 (system, line). The exact historical derivation is uncertain, but it is a modern technical coinage.