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Fault tolerance and types of faults
Short answer
Fault tolerance is the ability of a system to continue correct operation despite faults. Faults in distributed systems include crash (server halts), omission (lost messages), timing (response outside deadline), response (incorrect value), and arbitrary/Byzantine (malicious or arbitrary behavior).
What is fault tolerance? Explain different type of faults that may occur in a distributed system.
Fault tolerance
Fault tolerance is the property of a system to keep working correctly in the presence of faults, so that a fault does not become a failure of the whole service. It is achieved by redundancy and recovery.
Types of faults
A fault is the defect or cause (a broken component, a software bug, a bad link) that may lead to an error, an incorrect internal state. An error that reaches the service interface and makes the system deviate from its specification is a failure. By duration, faults are transient (occur once and vanish), intermittent (appear and disappear repeatedly) or permanent (persist until the component is repaired).
By the way a server fails, the failures are classified as:
| Type | Behaviour |
|---|---|
| Crash failure | The server halts, but worked correctly until it halted |
| Omission failure | Fails to respond to requests (receive omission) or to send replies (send omission) |
| Timing failure | Response comes outside the specified time interval |
| Response failure | Wrong value (value failure) or wrong state transition |
| Arbitrary (Byzantine) failure | Produces arbitrary responses at arbitrary times; may be malicious |
By source, faults can also be hardware, software, network or operator faults. In a distributed system, network faults such as lost messages, link failures and partitions are especially important.
Example: a server that stops responding has a crash failure, and a link that drops 5% of packets has an omission failure.
✓ Answer checked by Claude Opus 5.5 (high effort)
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