CORE METRICS
System Uptime
The percentage of time that a system is fully operational and available to users.
Uptime % = (Total Time - Downtime) / Total Time × 100
The percentage of time that a system is fully operational and available to users.
The Nines
- 99% (2 Nines): Down 3.65 days/year. (Okay for blogs).
- 99.9% (3 Nines): Down 8.76 hours/year. (Standard for SaaS).
- 99.99% (4 Nines): Down 52 minutes/year. (Enterprise grade).
- 99.999% (5 Nines): Down 5 minutes/year. (Telco/Critical Infrastructure).
Each additional "nine" is 10x harder to achieve. The cost of going from 99.9% to 99.99% is often not worth it for most applications.
ExSaaS Platform Availability Journey
"B2B SaaS improved from 99.8% to 99.95% uptime over 12 months. Key changes: Implemented database failover, added caching layer, and improved deployment process. Customer churn dropped from 12% to 6%."
Impact
Doubled ARR growth through improved trust and retention
Resolution
Multi-region architecture with automated failover
Why Uptime Matters
The primary measure of reliability.
Often expressed in "Nines" (e.g., 99.9%).
Common Pitfalls
Chasing 5 nines (99.999%) prematurely
Focus on 3-4 nines first. The cost of 5 nines is rarely justified for non-critical systems.
Measuring uptime only at the server level
Measure from the user's perspective. Use synthetic monitoring to test actual user flows, not just server pings.
Frequently Asked Questions
What does 99.9% uptime mean in hours?
99.9% uptime allows for 8.76 hours of downtime per year (43.8 minutes per month). This is the standard for most SaaS applications.
How many nines do I really need?
For most SaaS: 99.9% (3 nines) is sufficient. For critical infrastructure: 99.99% (4 nines). Each additional nine costs exponentially more.
What is the difference between uptime and availability?
Uptime measures if the system is running. Availability measures if users can successfully use the system. A site can be "up" but unavailable due to errors or slowness.