A 99.9% uptime SLA allows about 8.76 hours of unplanned downtime per year. Tier-III data centers use redundant power and cooling to reduce single points of failure. Understanding how SLA is measured and what is excluded helps you set expectations and compare providers.
What uptime SLA means
- 99.9% ≈ 8.76 hours of unplanned downtime per year (or ~43 minutes per month).
- 99.99% ≈ 52 minutes per year. Higher tiers usually cost more.
- Downtime is typically measured from the provider’s network or monitoring; read the exact definition.
What to check in the SLA
- Exclusions: Planned maintenance, force majeure, or client-side issues may be excluded from the calculation.
- Credits: How are service credits calculated and how do you claim them?
- Measurement: Is it per incident, monthly, or annual? What is the source of truth (monitoring, tickets)?
- Tier-III: Facilities with redundant power and cooling help meet high uptime; ask for certification or design details.
Summary
Read the SLA wording for exclusions and credit rules. Prefer providers that publish clear SLAs and offer tier-III or equivalent infrastructure. Combine SLA with support quality and transparency for a reliable production environment.
