Uptime percentages look almost identical on paper \xE2\x80\x94 99.9% vs. 99.99% \xE2\x80\x94 but the gap between them is the difference between a bad afternoon and barely noticing.
Translate the Nines Into Time
- 99% (two nines): ~3.65 days of downtime per year.
- 99.9% (three nines): ~8.8 hours per year.
- 99.99% (four nines): ~52 minutes per year.
- 99.999% (five nines): ~5 minutes per year.
Each additional nine cuts allowable downtime by ~10x. That's why "just one more nine" costs more \xE2\x80\x94 it's a big jump in commitment.
Match the tier to the stakes: a back office may be fine at three nines; payments, healthcare, or trading floors justify four or five \xE2\x80\x94 often achieved with redundant circuits, not a single line.
How Higher Uptime Is Achieved
Beyond a single carrier's SLA, the practical path to four/five nines is redundancy: diverse circuits from different carriers with automatic failover, so no single failure takes you down. See redundancy and failover.
Don't Pay for Nines You Don't Need
Higher tiers cost more. The goal is matching uptime to the real cost of downtime at each site \xE2\x80\x94 not buying five nines everywhere. We help right-size SLAs and design redundancy. See what an SLA covers and DIA.
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