shelf life of a disc

Disc Drive Shelf life Research Data expectation preservation

"Disk Failures in the Real World: What Does an MTTF of 1,000,000 Hours Mean to You?", by Bianca Schroeder and Garth A. Gibson, Carnegie Mellon
University, was awarded best paper (along with one other) at FAST 2007.

They actually went and got data to determine whether much of the conventional wisdom on disk drives is actually accurate -- and of course it wasn't.

Excerpt from the abstract:

In this paper, we present and analyze field-gathered disk replacement data from a number of large production systems, including high-performance computing sites and internet services sites. About 100,000 disks are covered by this data, some for an entire lifetime of five years. The data include drives with SCSI and FC, as well as SATA interfaces. The mean time to failure (MTTF) of those drives, as specified in their datasheets, ranges from 1,000,000 to 1,500,000 hours, suggesting a nominal annual failure rate of at most 0.88%.

We find that in the field, annual disk replacement rates typically exceed 1%, with 2-4% common and up to 13% observed on some systems. This suggests that field replacement is a fairly different process than one
might predict based on datasheet MTTF.

We also find evidence, based on records of disk replacements in the field, that failure rate is not constant with age, and that, rather than a significant infant mortality effect, we see a significant early onset
of wear-out degradation. That is, replacement rates in our data grew constantly with age, an effect often assumed not to set in until after a nominal lifetime of 5 years.

Interestingly, we observe little difference in replacement rates between SCSI, FC and SATA drives,...

Available online at
http://www.usenix.org/events/fast07/tech/schroeder.html