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DevOps and Security Glossary Terms

Service Reliability - Definition & Overview

What is service reliability?

Service reliability is a method for measuring the probability that a system, product, or service will maintain performance standards for a specific period of time.


  • Reliability is concerned with the probability of a piece of equipment functioning properly within a given time frame.
  • There are several ways to measure reliability, or the probability of system failures, that will have relevant impacts on your system, such as MTBF and MTTR.
  • There are three major types of reliability tests: feature testing, load testing, and regression testing.

Most important aspects of reliability

Some of the most important aspects of reliability include:

  • Probability of mission success

  • Performances will maintain their intended function or purpose

  • Service levels are performed to a specific degree of compliance and expectation

  • Service levels are maintained over a specific period of time, be it minutes, days, months, or cycles

  • The specified conditions within service level expectations are being met

Examples of reliability

There are several ways to measure the probability of system failures that will have relevant impacts on your system. A few common service reliability metrics include:

  • Mean time between failures
    • MTBF represents the average time between system failures or breakdowns. It is a crucial aspect of maintenance to measure the performance, design, and safety of important systems, such as generators or transportation vehicles.

  • Mean time to repair
    • MTTR shows the average time it takes to repair a technical or mechanical system, which includes both times to repair as well as testing time.

  • Mean time to recovery
    • MTTR (recovery) is a metric that represents the time it takes to recover from any system failures. Unlike repair time, MTTR takes into account how long it takes for products or systems to become fully operational again.

  • Mean time to resolve
    • MTTR (resolve) refers to how long it took to detect the failure, assess the issue, repair the issue, and also any time spent on ensuring that it isn’t a recurring failure. This, unlike the previous metrics, takes into account the long-term implications of failures and failure prevention.

Quality vs reliability

While we know that reliability looks at performance in relation to a specific duration of time or life cycle, quality is an important part of service level agreements that is often used interchangeably with reliability. However, there are some key differences between the two that can help you maintain your desired standards of service.

While reliability is more concerned with the probability of a piece of equipment functioning properly within a given time frame, availability measures the operational capabilities of a product to be operational when needed. Availability is expressed through the percentage of time that a system, solution, or infrastructure maintains its functionality within normal conditions.

The mathematical equation for availability is: operational availability = MTBM ÷ (MTBM + MMT + MLDT).

Testing reliability

So, as a reminder, reliability is the process of attaining a probability of success, durability, dependability, quality over time, and availability to perform a function over a specific period of time.

Reliability testing helps assess the before mentioned qualities in a standardized, metric/time-based manner.

Testing reliability helps teams:

  • Find patterns of repeated failures

  • Find the frequency in which failures occur within specific cycles or time periods

  • To identify the root cause of failures

  • And to apply performance tests of your various modules of software applications

There are major types of reliability tests, which are feature testing, load testing, and regression testing.

  • Features testing look at the different features provided by software in order to assess execution and reductions between two operations.

  • Load testing is utilized to assess the performance of software when it’s operating under maximum work-load conditions. This will help check for degradation that can occur over time.

  • Finally, regression testing identifies any new bugs as a result of resolving previous failures or errors. Every time an update is made of new software features, regression testing is performed.

Reliability in an SLA, SLO, and SLI

  • SLA
    • In order to maintain your service level agreements, which is a contract between a service provider and your customers or other service-level recipients, reliability has to be maintained. SLAs provide the language that is necessary to create a contract between two parties and is a measuring stick for keeping your end of the bargain within that contract.

  • SLO
    • A service level objective is a primary way to measure whether or not reliability is being achieved in maintaining your SLA. SLOs, through their validity periods, expressions, and quality of service, make it easier for SRE teams to evaluate and assess the functionality of their primary services and products.

  • SLI

Service level indicators refer to the various individual metrics that are measured to identify specific performance indicators. SLIs are the foundation on which SLOs are based, and they provide the concrete numbers as to how well various aspects of services

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Click here to learn more about how Sumo Logic can help you maintain reliability for now and for the future. Modern applications allow teams to deploy features fast while maintaining optimal reliability and customer experience. Learn more about application modernization.

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