Comparing MTBF, MTTF, MTTR

Posted by in Security+ | 0 comments

Metrics such as MTBF, MTTF, MTTR, and others are commonly used within risk management.  If you’re planning on taking the Security+ exam, you should have a good understanding of these metrics. For example, can you answer this question?

Q. Lisa is the new CTO at your organization. She wants to ensure that critical business systems are protected from isolated outages. Which of the following would let her know how often these systems will experience outages?

A. MITM

B. MTBF

C. MTTF

D. MTTR

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

MTBF, MTTF, MTTR and Risk Management

Risk management is the practice of identifying, monitoring, and limiting risks to a manageable level. It doesn’t eliminate risks, but instead identifies methods to limit or mitigate them. The amount of risk that remains after managing risk is residual risk.

Senior management is ultimately responsible for residual risk—the amount of risk that remains after mitigating risk. Management must choose a level of acceptable risk based on the organization’s goals.  They use a variety of tools and metrics to identify the risks, and then decide what resources (such as money, hardware, and time) to dedicate to manage the risk.

Some of the common metrics they use are:

  • Mean time between failures (MTBF)
  • Mean time to failure (MTTF)
  • Mean time to recover (MTTR)

What is Failure?

These metrics are important to understand when evaluating the failure rate of critical business systems. Typically, a critical business system will have multiple redundancies in place to ensure it stays operational even after a fault occurs. In other words, critical systems can tolerate faults without actually failing.

If a server has one hard drive, and the one hard drive fails, the server fails. This is a system failure.

However, if a server has a redundant array of independent disks 6 (RAID- 6), and one drive fails, the server continues to operate. This is not a system failure.

Mean Time Between Failures (MTBF)

The mean time between failures (MTBF) metric provides a measure of a system’s reliability and is usually represented in hours. More specifically, the MTBF identifies the average (the arithmetic mean) time between failures.

Higher MTBF numbers indicate a higher reliability of a product or system. Administrators and security experts attempt to identify the MTBF for critical systems with a goal of predicting potential outages.

Mean Time to Failure (MTTF)

The mean time to failure (MTTF) is the length of time you can expect a device to remain in operation before it fails. It is similar to MTBF, but the primary difference is that “between” in the MTBF metric indicates you can repair the device after it fails.

In contrast, the MTTF metric indicates that you will not be able to repair a device after it fails. It is permanent. For example, the MTTF of a power supply within a server indicates how long the power supply may last before it fails and needs to be replaced.

Mean Time to Recover (MTTR)

The mean time to recover (MTTR) identifies the average (the arithmetic mean) time it takes to restore a failed system. In some cases, people interpret MTTR as the mean time to repair, and both mean essentially the same thing.

Organizations that have maintenance contracts, such as service level agreements (SLEs), often specify the MTTR as a part of the contract. The supplier agrees that it will, on average, restore a failed system within the MTTR time.

The MTTR does not provide a guarantee that the supplier will restore the system within the MTTR every time. Sometimes it may take a little longer and sometimes it may be a little quicker, with the average defined by the MTTR.

MTBF, MTTF, MTTR Summary

As a short summary these metrics are:

  • Mean time between failure (MTBF) –  provides a measure of a system’s reliability and identifies the average time between failures. It is often used to predict potential outages with critical systems.
  • Mean time to failure (MTTF) – the length of time you can expect a device to remain in operation before it fails. It indicates failure is permanent, while MTBF indicates it can be repaired.
  • Mean time to repair (MTTR) – the average time it takes to restore a failed system.

mtbf


Security+ Practice Test Questions

SY0-501 Practice Test Questions 

Over 300 realistic Security+ practice test questions

All questions include explanations so you'll know why the correct answers are correct,

and why the incorrect answers are incorrect.

Pass the Security+ Exam

the First Time You Take It

Multiple quiz formats to let you use these questions based on the way you learn.
  • Learn mode - randomized. View each of the questions in random order. Learn mode allows you to keep selecting answers until you select the correct answer. Once you select the correct answer, you'll see the explanation. Click here to see how learn mode works.
  • Learn mode - not randomized. View each of the questions in the same order. Use this if you want to make sure that you see all of the questions. Learn mode allows you to keep selecting answers until you select the correct answer. Once you select the correct answer, you'll see the explanation. Click here to see how learn mode works.
  • Test mode - randomized. View each of the questions in random order. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.
  • Test mode - not randomized. View each of the questions in the same order. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.
  • Test mode - 75 random questions. View 75 random questions from the full test bank similar to how the Security+ exam has a potential maximum of 75 multiple choice questions. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.

Get the full bank of SY0-501 Practice Test Questions Here

 SY0-501 Practice Test Questions


INCLUDES QUESTIONS TO HELP YOU PREPARE

FOR THE NEW PERFORMANCE BASED QUESTIONS 

Bonus - Performance Based Questions

Three sets of performance-based questions including over 30 questions. These questions show you what you can expect in the live exam. They include drag and drop, matching, sorting, and fill in the blank questions. See a demo here.

Bonus - Extra Practice Test Questions

New multiple-choice questions in the extra test bank. Questions are added occasionally. You can see what has been added recently here.

Get the full bank of Security+ (SYO-501) Practice Test Questions Here

Get the full bank of Security+ Practice Test Questions

Click here if you're looking for SY0-501 Full Study Package

Q. Lisa is the new CTO at your organization. She wants to ensure that critical business systems are protected from isolated outages. Which of the following would let her know how often these systems will experience outages?

A. MITM

B. MTBF

C. MTTF

D. MTTR

B is correct. The mean time between failures (MTBF) provides a measure of a system’s reliability and is usually represented in hours. More specifically, the MTBF identifies the average (the arithmetic mean) time between failures. In the context of this scenario, it provides an estimate of how often the systems will experience outages.

A is incorrect. Man in the middle (MITM) is an attack allowing the attacker to intercept traffic and insert malicious code sent to other clients.

B is incorrect. The mean time to failure (MTTF) indicates the lifetime of an item. In other words, it provides an estimate of how long the item will remain operational before it failures. MTTF typically indicates a permanent failure of a device, such as the failure of a hard drive, requiring replacement of the component.

D is incorrect. The mean time to repair (MTTR) refers to the time it takes to repair a system, not the time between failures.

See Chapter 8 of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide for more information on risk management and risk calculations.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.

CompTIA Security+ Get Certified Get Ahead: SY0-501 Study Guide

Subscribe To Our Newsletter

Join our mailing list and get a free excerpt of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide.  This excerpt includes the introduction and Chapter 1. 

You have Successfully Subscribed!

Get Certified Get Ahead is a participant in the Amazon Services LLC Associates Program,
an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.

Copyright © 2015 Get Certified Get Ahead. All Rights Reserved.