A customer has an HP D6000 Disk Enclosure with 70 LFF Universal SAS drives. Assuming that the mean time between failure (MTBF) of a single disk is 1,400,000 hours, what is the MTBF of the full array?

In a series reliability model, each additional disk is an independent failure point, so the system MTBF decreases proportionally with the number of drives. With 70 drives each rated at 1,400,000 hours MTBF, the array MTBF = 1,400,000 / 70 = 20,000 hours. This formula reflects the statistical reality that adding more drives increases the probability of any single drive failing within a given time period.

40,000 hours would be the result of dividing 1,400,000 by 35 drives, not the actual 70 drives in the enclosure.

700,000 hours would incorrectly result from dividing by only 2 drives rather than the full 70-drive count.

1,400,000 hours is the MTBF of a single individual disk and does not account for the compounded failure probability introduced by having 70 drives in the array.