Traditional HDD specifications may not reflect properly HDD failure rate.
Recently published studies of large HDD populations indicate that actual failure rate exceeds several times those quoted by specifications. They also indicate that failure probability is increasing with HDD age, starting already at the second year of operations.
For example, in the study conducted by Google
(1) , almost 2% of deployed HDDs had to be replaced during the first year of operation. This number was approximately 8% for the second and more than 8% the third year of operations. These failure rates did not account for prior to deployment burn-in failures.
Similar Carnegie Mellon study
(2) concluded that the actual failure rate is 2-10 times greater than suggested by HDD datasheet and is also HDD age dependent. The study analyzed failure data for SATA, FC and SCSI drives. It concluded that operational conditions, usage and environmental factors affect HDD failure rate much more than HDD components itself.
These findings provide a real life view on the HDD reliability in controlled environmental conditions found in data centers.
It has to be noted that HDD wear-out time depends on number of factors such as temperature, vibration, duty cycle and power on time.
Read more about writing endurance
(1) Failure trends in a large disk drive population, Feb 2007, E. Pinheiro et al, Google
(2) Disk Failure in the real world: What does an MTTF of 1,000,000 hours mean to you? B.Schroeder et al, FAST'07;Carnegie Mellon University
