disk drive failure rates

[David Farber <dave () farber net>]

Begin forwarded message:

From: Rod Van Meter <rdv () tera ics keio ac jp>
Date: March 7, 2007 8:36:12 PM EST
To: David Farber <dave () farber net>
Subject: disk drive failure rates
Reply-To: rdv () tera ics keio ac jp

Dave,

(Personal, but feel free to forward to IP if you wish.)

"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

                --Rod




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