Agreed on both points.
Of course, if you are doing a failure analysis it is something of a
professional obligation to be somewhat pessimistic. For one thing, being
pessimistic on the factors you know about may compensate to some degree for
your inadvertent optimism regarding the factors you don't know about or
think are minor.
In general, assuming stable distributions with finite variance is a bit
dangerous in any case. On the other hand, doing any real modeling with Levy
distributions is hard enough that you probably gain less insight for being
more correct. It is worth incorporating correlated failures into your model
if you can but even that is non-trivial.
On Wed, Aug 10, 2011 at 12:31 PM, Brian Bockelman wrote:
> Ted is assuming a MTTF of 25kHours; I think that's overly pessimistic,
> although both papers indicate that MTTF is a crappy way to model disk
> lifetime.
>