What Is MTTF?

What Is MTTF?

Mean time to failure, or MTTF, is a metric that measures the average time between non-repairable failures for a given technology asset, such as a device, system, or application.

MTTF can help you understand the average lifespan of a product, system, or device, including CPUs, hard drives, IoT devices, or network switches. The metric is also used to compare performance between an old and new system, determine expected system lifetimes, and schedule maintenance.

MTTF only records one failure per asset and measures the mean over a long period for many assets. Increasing the number of assets observed will increase the accuracy of MTTF.

MTBF vs. MTTF: Which Metric to Use?

Mean time to failure and mean time before failure (MTBF) both measure time to help you evaluate the performance of an asset, though they apply to different types of assets.

MTBF vs. MTTF: Key Differences

MTTF is the average time it takes an asset to fail the first and only time, and it only applies to assets that must be replaced upon failure. In this case, replacing the asset is the only way to fix the problem; once MTTF is reached, the asset has reached its maximum hours of operation.

MTBF, on the other hand, is the average time it takes an asset to fail the first time, meaning that it’s specific to assets that can be repaired. Since the system is repairable, it can fail again, with MTBF representing the average time between each failure.

Thus, the key difference between MTTF and MTBF is that with MTTF, the issue can only be fixed by replacing the asset. With MTBF, the issue can be fixed by repairing the asset.

When to Use MTBF

Operations and reliability teams can use MTBF to evaluate the performance of equipment and systems. By comparing the performance of similar equipment operating under similar conditions, they can assess failures and design preventative maintenance plans. 

In addition, MTBF is often used to monitor the progress of reliability programs. An increasing MTBF is a sign that systems and equipment are becoming more reliable.

How to Calculate MTTF: Step-by-Step Formula

MTTF is calculated by adding the total lifespan of all the devices you’re assessing and dividing it by the number of devices. Here’s the general formula:

MTTF = total lifespan across devices / total number of devices

First, determine the total number of devices, then determine the lifespan of each device. For example, let’s say you have three similar hard drives in a RAID configuration and that the lifespans of each hard drive are three, four, and five years, respectively.

In this case:

  • Total number of devices = 3
  • Total operational hours = (3 + 4 + 5) = 12 years
  • MTTF = 12 / 3 = 4 years

What Tools Do You Need to Monitor MTTF?

Software tools are often used to measure MTTF and other reliability metrics.

These monitoring applications, along with metrics, logs, and tracing—the pillars of observability—help teams identify issues in systems and components that may lead to failure faster. There are several open source and commercial tools available, including Prometheus, Datadog, Splunk, and OpenTelemetry.

Automated workflows can also help teams detect, handle, and resolve issues faster. Automation can be used to alert the right teams of an issue, document the issue and mitigation process, and order replacement parts.

What Is a Good MTTF?

MTTF is especially important if a system or component is integral to the operation of your business. The longer the MTTF, the better. A short MTTF means that your system is more prone to failures and downtime, which could affect application and service delivery, customer satisfaction, and revenue.

How to Increase MTTF for Reliability

A good MTTF estimation can help dramatically improve system reliability. If you know when a resource is likely to fail, you can replace it before failure occurs. A few other ways to increase MTTF for reliability include:

  • Proactive maintenance: Have spare parts and equipment available so that teams can make replacements without delay. Keep assets and equipment in good condition with a planned replacement schedule, and continually review and improve preventative maintenance processes.
  • Documentation: When issues occur, document their root cause, identification measures, and any remediation steps taken to prevent them from happening again.
  • Implementing redundancy: Optimize hardware redundancy with the use of RAID, redundant switches, and other technology to reduce the impact of failure.

MTTF Calculation Examples

Let’s look at examples of low, average, and high MTTF for different sets of devices that each have an expected lifetime of 20,000 hours or less.

High MTTF

Device 1 has a lifespan of 15,000 hours, Device 2 has a lifespan of 19,000 hours, Device 3 has a lifespan of 18,000 hours, and Device 4 has a lifespan of 20,000 hours.

Total number of devices = 4
Total operational hours = (15,000 + 19,000 + 18,000 + 20,000) = 72,000 hours
MTTF = 72,000 / 4 = 18,000 hours

Average MTTF

Device 1 has a lifespan of 9,000 hours, Device 2 has a lifespan of 11,000 hours, Device 3 has a lifespan of 15,000 hours, and Device 4 has a lifespan of 19,000 hours.

Total number of devices = 4
Total operational hours = (9,000 + 11,000 + 15,000 + 19,000) = 54,000 hours
MTTF = 54,000 / 4 = 13,500 hours

Low MTTF

Device 1 has a lifespan of 10,000 hours, Device 2 has a lifespan of 11,000 hours, Device 3 has a lifespan of 8,000 hours, and Device 4 has a lifespan of 9,000 hours.

Total number of devices = 4
Total operational hours = (10,000 + 11,000 + 8,000 + 9,000) = 38,000 hours
MTTF = 38,000 / 4 = 9,500 hours

Who Should Use MTTF and When?

MTTF is a useful reliability metric in several areas of technology, including cybersecurity, incident response, and DevOps.

How to Use MTTF in Cybersecurity

A cybersecurity event can refer to anything that differs from normal system behavior, such as a suspicious email or software download. The event could be harmless, but it also has the potential to compromise the system. In cybersecurity, MTTF would show that security mechanisms have failed to prevent an attack.

How to Use MTTF in Incident Response

Incident response is used by IT professionals to respond to security incidents, such as a successful cyberattack.

MTTF in incident response shows how long the infected system can run until it shuts down. It lets the team know how much time they have to put failover or additional security measures in place to prevent further loss or damage.

How to Use MTTF in DevOps

Tracking MTTF in DevOps can help teams understand the reliability of a system or application deployment. For example, MTTF can indicate the average time between detection of a defect in a system or an application and complete failure, which can help DevOps teams prepare for system failures.

Calculating MTTF and other reliability metrics for cybersecurity, incident response, and DevOps requires massive amounts of real-time and historical data. Observability and monitoring tools need ultra-fast, high-performance storage to support complex queries and process data in real time.

Pure Storage® FlashBlade® is the industry’s most advanced all-flash storage solution for fast file and object data. FlashBlade provides the speed and performance levels you need to gather quality MTTF metrics.

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