SLA and Availability Calculation | IT Passport Exam Prep

What is an SLA?

SLA stands for Service Level Agreement. It is a document that guarantees the quality of a service in numerical terms between a service provider and a user. It plays a central role in ITIL service management (see What is ITIL).

Key Metrics Listed in an SLA

Availability

Availability refers to the percentage of time a service is operating normally. The formula is MTBF ÷ (MTBF + MTTR) × 100%. MTBF stands for Mean Time Between Failures, and MTTR stands for Mean Time To Repair.

Response Time

Response time is the time from sending a request to receiving the first response.

Throughput

Throughput refers to the number of items that can be processed per unit of time.

Recovery Time Objective (RTO)

The Recovery Time Objective is the target time for recovery after a failure occurs (explained in detail in What is BCP).

Availability and Annual Downtime Conversion

Each additional nine reduces the downtime by a factor of 10. A common exam question is, "How many hours of downtime per year does 99.9% availability allow?" The answer is approximately 8.76 hours.

Availability Calculation Example

If one year is 365 days (8760 hours), then 8.76 hours of downtime results in 99.9% availability. Also, if MTBF is 100 hours and MTTR is 1 hour, the availability is calculated as 100 ÷ 101 × 100, which is approximately 99%.

Provisions for SLA Violations

When an SLA is violated, penalty clauses typically stipulate a reduction in service fees. Additionally, incident reporting obligations require a report on the cause of the violation.

Key Points for the IT Passport Exam

Be sure to memorize the availability formula (MTBF ÷ (MTBF + MTTR)). The annual downtime for 99.9% availability is approximately 8.76 hours. The difference between SLA and SLM (Service Level Management) is also a frequently tested point.

Typical Past Exam Question Patterns

• "What is the availability when MTBF = 100 and MTTR = 5?"
• "What is the approximate annual allowable downtime for 99.99% availability?"

Related Terms

• ITIL Service Management (What is ITIL)
• BCP RTO/RPO (What is BCP)
• Facility Management (Facility Management)

Study Tips

It helps to memorize the availability formula by saying it out loud: "MTBF divided by (MTBF plus MTTR)." Also, remember the relationship that "each additional nine reduces downtime by a factor of 10." Memorize "99.9% = 8.76 hours/year" as a single phrase.

Summary

By understanding the availability formula and the relationship between the number of nines and downtime, you can reliably score points on SLA-related questions. For comprehensive practice on the Management domain, see the Management Summary; for full-length practice, use the Mock Exam.