Majority Quorum Availability Calculator
Estimate whether a majority of replicas are available using a binomial model and explicit independent, equal-availability assumptions.
This probability model does not represent correlated infrastructure failures. Maintained by Buildopsy · Updated .
Replica availability scenario
Use 1–25 replicas. A majority is the smallest number greater than half of the configured replicas.
Formula and assumptions
For n identical independent replicas with per-replica availability p, majority quorum is q = floor(n / 2) + 1. Quorum availability is Σ C(n,k) pᵏ (1−p)ⁿ⁻ᵏ for k = q…n.
This is a mathematical model, not a service-level prediction. Replica failures are rarely fully independent: shared zones, networks, control planes, software releases, and dependencies can dominate. It also excludes recovery time and quorum protocol behavior. Use fault-domain design and observed failure data in addition to this estimate.
Frequently asked questions
How is quorum availability calculated?
The calculator sums the probability of all combinations with at least a strict majority of available replicas, assuming the same independent availability for each replica.
Does replica count alone guarantee high availability?
No. Independence is a simplifying assumption; correlated failures, shared dependencies, and recovery behavior must be assessed separately.
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