Data availability is fundamentally expressed as a ratio: the amount of time a system was actually operational and accessible (uptime) relative to the total time it was expected to be operational, which by extension requires accurately capturing the amount of time it was not operational (downtime). Monitoring uptime (A) provides the direct measurement of how long systems were successfully available and functioning, forming one half of the availability equation. Calculating total downtime (B) provides the complementary measurement, capturing every period the system was unavailable, whether due to failure, maintenance, or other disruption, which is subtracted from total elapsed time to compute the availability percentage. Together, uptime and downtime are the two foundational, directly measurable inputs from which any meaningful availability metric (such as the standard formula of uptime divided by total time) is derived, making this pairing the correct answer. Excluding the time during backup restore (C) would artificially distort the availability calculation by omitting a period during which systems were arguably unavailable to normal use, undermining the accuracy of the measurement rather than contributing a valid, standard method for calculating availability. Calculating the mean time to report an incident (D) measures how quickly an issue is identified and communicated, a useful operational responsiveness metric, but it measures detection speed, not the actual proportion of time a system was available, making it unrelated to the availability calculation itself. Uptime and downtime are correct.

Reference topic: Managing the Data Protection Environment - Measuring Data Availability.