Define the number of simultaneous failures
Synthetic copies are A1/A2 in domain A, B1 in B and C1 in C. A failed domain removes its copies. Requirement is one surviving copy after any two distinct domain failures. Only A/B/C failures are modeled.
| Failed domains | Survivors | Count |
|---|---|---|
| A+B | C1 | 1 |
| A+C | B1 | 1 |
| B+C | A1,A2 | 2 |
Enumerate distinct domain pairs
- List every distinct pair
- Remove copies in either failed domain
- Take the minimum survivor count
Two copies in one domain are removed together; they are not two failure tolerances.
What is the worst-case survivor count, and would removing C1 preserve the rule?
Show the worked answer
One, so the full inventory passes. Removing C1 makes A+B failure leave zero and fails. Additional A copies would not replace missing domain C.
Check the worst pair
| Case | Decision | Reason |
|---|---|---|
| Three-domain inventory | Pass | Every pair leaves≥1 |
| Remove C1 | Fail | A+B leaves 0 |
Retain all three pair results in the worksheet. Testing only B+C would overstate the resilience of an A-heavy inventory.