Mean Time to Repair (MTTR)
Fault and Failure Metrics are becoming essential parameters for performance testing, load testing, and other kinds of non-functional software testing. The main goal of measuring and tracking these metrics is to create robust software components that can maintain high-performance levels even under heavy traffic or network fluctuations. Mean Time to Repair (MTTR) is one of the most important Faults and Failure Metrics today.
Furthermore, developers and IT teams are interested in measuring software reliability with Mean Time Between Failures (MTBF). The MTBF is essentially the sum of the aforementioned MTTR and Mean to Failure (MTTF), which is essentially the difference of time between two consecutive failures. This is the benchmark for reducing the number of failures and improving incident management.
MTBF = MTTF + MTTR
By calculating and monitoring these metrics, companies can improve repair times, reduce lifecycle costs, and eliminate unplanned downtime.
- Reliability – This basically refers to the probability that a software component will perform its intended function without failure for a pre-defined time period. This quality is also closely related to design and coding. Fault and Failure Metrics that have been mentioned earlier in this page are often used to measure and predict component and system reliability.
- Maintainability – This describes the ease with which a system can be fixed and restored to full operation following a failure. Maintainability depends on a host of factors, including the product’s quality, resources and staffing, and the efficiency of repair procedures. MTTR is one of the benchmark metrics used to determine maintainability (low is better.).
- Availability – This is the probability that a system is operating as designed when required. A function of reliability and maintainability, it’s calculated by dividing MTBF by the sum of MTBF and MTTR, a pretty straightforward one.
Availability (A) = MTBF / (MTBF + MTTR)
How to Calculate MTTR?
Before we dive into the specifics of calculating MTTR, you need to set up the infrastructure required and introduce cross-department procedures. This includes diagnosis procedures, damage control protocols, and communication channels.
MTTR is calculated by dividing the total downtime caused by failures by the total number of failures. For example, if a system fails twice in a month, and the failures resulted in a total of six hours of downtime, the MTTR will stand at 3 hours. While repairs can sometimes take minutes, days, or weeks to complete, MTTR is usually measured in hours depending on the failure severity.
MTTR = 6 hours / 2 failures = 3 hours
Other Key Product Metrics
Besides the aforementioned benchmarks, you will need to keep track of the following performance testing metrics to achieve sustainable quality and speed.
- Size of the Software: – Line of Code (LOC) is a universal metric today, where the source code is counted (no comments or non-executable statements).
- Function Point Metric: This method measures the functionality delivered to the user and is independent of the programming language.
- Complexity: This complexity-centric metric determines the complexity of the app’s control structure by simplifying the code into a graphical representation.
- Test Coverage Metrics: It estimates fault and reliability by performing the complete test of software products.