A vendor-quoted MTBF implies that half the drives in a large population will fail within that time of operation. For example, a common specification for PATA and SATA drives may be 300,000 MTBF, implying that in a 600,000 drive sample, one drive failure may occur per hour if failures were evenly distributed, translating to 8760 drive failures per year or a theoretical 1.46% annualized failure rate.
Seagate estimates the MTBF for a drive as the number of power-on hours per year divided by the first year AFR. The AFR for a drive is derived from time-to-fail data from a reliability-demonstration test (RDT).
The relationship between AFR and MTBF is:
- (expressed in %)
Google's 2007 study found that actual AFRs for individual drives ranged from 1.7% for first year drives to over 8.6% for three-year old drives.
Read more about this topic: Annualized Failure Rate
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