1. What is System Availability?

System availability is a metric that measures the percentage of time a system is operational and available for use. It's a key performance indicator for IT systems, networks, and services.

2. How Does the Calculator Work?

The calculator uses the availability equation:

Where:

• \( Downtime \) — Total time system was unavailable (hours)
• \( Total \) — Total time period being measured (hours)

Explanation: The equation calculates the percentage of time the system was available during the measured period.

3. Importance of Availability Calculation

Details: System availability is crucial for service level agreements (SLAs), capacity planning, and reliability engineering. High availability (typically 99.9% or higher) is often required for critical systems.

4. Using the Calculator

Tips: Enter downtime and total time in hours. Both values must be positive numbers, and total time must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is considered good availability?
A: "Five nines" (99.999%) is considered excellent, meaning about 5 minutes downtime per year. 99.9% ("three nines") is about 8.76 hours downtime per year.

Q2: How is this different from reliability?
A: Availability measures uptime percentage, while reliability measures the probability of failure-free operation over a specific time period.

Q3: Should planned maintenance be counted as downtime?
A: It depends on your SLA. Some agreements exclude planned maintenance from availability calculations.

Q4: What time period should I use for calculation?
A: Common periods are monthly or yearly, but choose what makes sense for your monitoring needs.

Q5: How can I improve system availability?
A: Strategies include redundancy, failover systems, regular maintenance, and robust monitoring.