The Failover Recovery Chain
Ada re-derives this chapter’s own numbers step by step, at full precision
ADA · CALCULATION AUDIT
The Failover Recovery Chain
Across 40 hectares of vineyard whose sensors report every 300 s, losing a link without a backup route means an 8,100 ms outage — but a pre-cached backup collapses that to 167 ms, a 48.5x improvement that cuts the data at risk in one reporting cycle from 2.70% to 0.056%. The headline is a multi-second outage turned into a blip. This audit adds up each detect-switch-first-packet stage and asks whether that 48.5x figure holds, given it rests entirely on an assumed 8-second discovery estimate.
Companion to the chapter Ad-Hoc Production Readiness — every number here comes from that chapter.
Ada: The multi-path claim rests on turning a multi-second outage into a sub-second blip, and the chapter puts a number on it: 167 ms recovery with a pre-cached backup versus about 8 seconds without. Recovery is a sequence, though, so I will add each stage the chapter measured and check the improvement factor against the vineyard’s 300-second reporting cadence.
- With pre-cached backup:
100 ms detection + 5 ms cache lookup + 62 ms first packet = 167 ms. - Without backup:
100 ms detection + 8,000 ms route discovery = 8,100 ms. - Improvement factor:
8,100 / 167 = 48.5xfaster. - Exposure of one 300 s reporting cycle: single-path
8.1 / 300 = 2.70%; multi-path0.167 / 300 = 0.0557%. - Loss ratio:
2.70 / 0.0557 = 48.5xless data at risk — the same factor, as it must be.
The audit confirms the headline: a pre-cached backup collapses the outage from 8,100 ms to 167 ms, cutting the exposure of any single reporting cycle from 2.70% to 0.056%. That 48.5x reduction is the whole point, and it is only as sound as the 8-second discovery estimate it replaces — recovery is a measured sequence of detect, switch, and first-packet stages, so each stage must be timed rather than assumed.
Every number above is taken from the chapter’s own material and re-derived step by step.