What disaster recovery metric is total hours of operation divided by units?
Which of the following disaster recovery concepts is calculated by dividing the total hours of operation by the total number of units?
Community Votes
67% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The exam tests whether you can separate MTBF (reliability, based on uptime/failure count) from MTTR (maintainability, based on downtime/repair count); the trap is confusing repair or failure language because MTTR relates to time to restore, not operating time.
MTBF (Mean Time Between Failures) is the reliability metric calculated by dividing total operating hours by the number of failures or failed units. Community consensus strongly favors option B, distinguishing MTBF as a measure of time between failures rather than MTTR, which measures repair time.
A. MTTR is the most common wrong answer; learners mistakenly associate 'units' with failed units needing repair, but MTTR is computed from total downtime divided by number of repairs, not total hours of operation divided by failures.
Community Discussion (3 comments)
Comments & Corrections
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Expert Analysis
Why the Answer Is Correct
MTBF (Mean Time Between Failures) is a reliability metric that tells you the average amount of time a system operates before it fails. It is calculated as total operating time divided by the number of failures, which matches the question's intended formula of total hours of operation divided by total number of units (or failed units). Comment [1] correctly explains that MTBF measures average operating time before failing, and comment [2] reinforces that MTBF is calculated by dividing total hours of operation by the total number of failures. Therefore, B is the correct choice.
Why the Other Options Are Wrong
A. MTTR (Mean Time To Repair) is the average time required to repair a failed system, calculated by dividing total downtime by the number of repair events, not total operating hours. RPO (Recovery Point Objective) defines tolerable data loss measured in time, while RTO (Recovery Time Objective) defines maximum acceptable downtime to restore service; neither is a ratio of operating hours to failures. Comment [3] incorrectly applies MTTR to this formula, but the formula in the question uses operating hours, not downtime, so MTTR cannot be correct.
Community Comment Notes
The comments show clear consensus for B (67 votes versus 33 for A), and the reasoned explanations in [1] and [2] align with industry definitions of MTBF. A useful caution from the discussion is that the wording 'total number of units' is imprecise—it likely means 'total number of failures' or 'failed units.' That flawed phrasing may lead some test-takers to pick MTTR, but a strong understanding of reliability versus maintainability keeps the answer anchored to MTBF.
Official Reference
Exam Strategy
Look for formula keywords: if the question mentions operating/uptime hours divided by failure counts, choose MTBF; if it mentions downtime divided by repair counts, choose MTTR. Also remember RPO and RTO are time-based recovery targets, not ratio calculations, so they are usually easy to eliminate in these formula-style questions.
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