What is MTTR (mean time to repair)?
The average time it takes to repair a failed system or device and return it to a usable state (Mean Time To Repair). It includes the time to detect the failure, isolate the cause, replace parts or fix the settings, and verify the result. Availability is expressed as MTBF ÷ (MTBF + MTTR), so the shorter the MTTR, the higher the availability. It is shortened by monitoring that detects failures quickly, spare parts on hand, well-prepared procedures and automatic failover.
Japanese name: MTTR(平均修復時間)
MTTR (mean time to repair) appears in 4 practice questions across 3 topics, including IT Service Management and Systems Audit, Yield and quality control, Reliability.
Field: IT Service Management and Systems Audit
Calculating it from records
From the operating records of a period, MTTR is the total downtime divided by the number of failures. For example, if a system was down for a total of 6 hours in 3 failures during 720 hours, MTTR is 6 ÷ 3 = 2 hours, and MTBF is the operating time of 714 hours ÷ 3 = 238 hours. The availability is 238 ÷ (238 + 2) ≈ 0.992, which matches the fraction of time in operation, 714 ÷ 720.
Ways to shorten the MTTR
Repair time can be divided into the time to notice the failure, to isolate the cause, to fix it and to confirm correct operation. Monitoring detects and reports failures immediately, configuration management information and logs quickly identify the affected equipment, spare parts or standby systems cut the time for replacement or switchover, and documented procedures let anyone carry out the work the same way. In a configuration that switches automatically to a standby system, the outage seen by users can be shortened greatly.
FAQ
What does the "R" in MTTR stand for?
It usually stands for repair, giving mean time to repair. In IT services it is also used in the sense of restore or recovery, the time until users can use the service again, so which interval is counted should be checked against the definition in the SLA or similar document.
How does MTTR differ from RTO (recovery time objective)?
MTTR is the average of the time actually taken for repairs, a value that describes past performance. RTO is the target for how long it may take to resume a business process or system after a disaster or failure, a value decided at the planning stage.