Hard drive MTBF and AFR
This article is copied from Seagate website: Hard disk drive reliability and MTBF / AFR, for I'll use it as reference for my other articles. Indeed, it's good and easier for users to calculate the probability failure rate of a disk array.
Seagate is no longer using the industry standard "Mean Time Between Failures" (MTBF) to quantify disk drive average failure rates. Seagate is changing to another standard: "Annualized Failure Rate" (AFR).
Seagate is no longer using the industry standard "Mean Time Between Failures" (MTBF) to quantify disk drive average failure rates. MTBF has proven useful in the past, but it is flawed.
To address issues of reliability, Seagate is changing to another standard: "Annualized Failure Rate" (AFR).
MTBF is a statistical term relating to reliability as expressed in power on hours (p.o.h.) and is often a specification associated with hard drive mechanisms.
Seagate's new standard is AFR. AFR is similar to MTBF and differs only in units. While MTBF is the probable average number of service hours between failures, AFR is the probable percent of failures per year, based on the manufacturer's total number of installed units of similar type. AFR is an estimate of the percentage of products that will fail in the field due to a supplier cause in one year. Seagate has transitioned from average measures to percentage measures.
MTBF quantifies the probability of failure for a product, however, when a product is first introduced: this rate is often a predicted number, and only after a substantial amount of testing or extensive use in the field can a manufacturer provide demonstrated or actual MTBF measurements. AFR will better allow service plans and spare unit strategies to be set.
Hard drive reliability is closely related to temperature. By operational design, the ambient temperature is 86°F. Temperatures above 122°F or below 41°F, decrease reliability. Directed airflow up to 150 linear feet/min. is recommended for high speed drives.
Here is an example excerpt from a Product Manual, in this case for the Barracuda ES.2 Near-Line Serial ATA drive:
The product shall achieve an Annualized Failure Rate - AFR - of 0.73% (Mean Time Between Failures - MTBF - of 1.2 Million hrs) when operated in an environment that ensures the HDA case temperatures do not exceed 40°C. Operation at case temperatures outside the specifications in Section 2.9 may increase the product Annualized Failure Rate (decrease MTBF). AFR and MTBF are population statistics that are not relevant to individual units.