Faulttoleranta

Faulttoleranta, or fault tolerance, is the ability of a system to continue operating correctly even when part of the system fails. It aims for uninterrupted service or graceful degradation in the face of hardware faults, software bugs, human error, or external disturbances. Fault-tolerant designs are common in safety-critical and high-availability environments, where downtime or data loss can be costly or dangerous.

Core techniques include redundancy, error detection and correction, and failover mechanisms. Redundancy can be hardware (duplicate power supplies, mirrored storage with RAID, redundant processors) or software (multiple independent services). Error detection and correction use checksums, parity, or ECC memory to identify and recover from data corruption. Failover and hot standby configurations allow a backup component to take over with minimal interruption. Diversity in design (for example, N-version programming) reduces the risk that a single fault compromises all implementations.

In distributed and computing systems, fault tolerance often relies on data replication, consensus protocols, and regular checkpoints. Replication maintains multiple copies of state, while consensus algorithms (such as Paxos or Raft) enable agreement on a consistent state despite failures. Checkpointing and restart techniques enable recovery from a known good state after a fault. Systems may also employ time redundancy and retry logic to recover from transient faults.

Key metrics include availability (uptime percentage), mean time between failures (MTBF) and mean time to repair (MTTR). Fault-tolerant design involves trade-offs among cost, performance, and complexity, and is distinct from, though related to, high availability. It is widely applied in storage systems, networks, control systems, and safety-critical software.